> For the complete documentation index, see [llms.txt](https://nec-license.gitbook.io/books/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://nec-license.gitbook.io/books/2.-digital-logic-and-microprocessor/mcqs/mcqs-on-digital-logic/set-5.md).

# set-5

#### 201. A combinational logic circuit which generates a particular binary word or number is:

1. $$\text{Decoder}$$
2. $$\text{Encoder}$$
3. $$\text{Multiplexer}$$
4. $$\text{De-multiplexer}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$\text{Encoder}$$

**Explanation:**

* An encoder generates a specific binary word or number based on the input signals.

</details>

#### 202. Parallel adders are:

1. $$\text{Combinational logic circuits}$$
2. $$\text{Sequential logic circuits}$$
3. $$\text{Both of the above}$$
4. $$\text{None of the above}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$\text{Combinational logic circuits}$$

**Explanation:**

* Parallel adders are combinational circuits that perform addition without any memory or feedback.

</details>

#### 203. A de-multiplexer is also known as:

1. $$\text{Data selector}$$
2. $$\text{Multiplexer}$$
3. $$\text{Data distributor}$$
4. $$\text{Encoder}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$\text{Data distributor}$$

**Explanation:**

* A de-multiplexer distributes a single input signal to one of many output lines, hence it is also called a data distributor.

</details>

#### 204. A multiplexer is known as:

1. $$\text{Coder}$$
2. $$\text{Data selector}$$
3. $$\text{Decoder}$$
4. $$\text{Encoder}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$\text{Data selector}$$

**Explanation:**

* A multiplexer selects one of many input signals and forwards it to a single output line, hence it is also called a data selector.

</details>

#### 205. A flip-flop can store:

1. $$\text{One bit of data}$$
2. $$\text{Three bits of data}$$
3. $$\text{Two bits of data}$$
4. $$\text{Any number of bits of data}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$\text{One bit of data}$$

**Explanation:**

* A flip-flop is a basic memory element that can store one bit of data (either 0 or 1).

</details>

#### 206. Which of the following input combinations is not allowed in an SR flip-flop?

1. $$S=0, R=0$$
2. $$S=1, R=0$$
3. $$S=0, R=1$$
4. $$S=1, R=1$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$S=1, R=1$$

**Explanation:**

* The input combination ( S=1, R=1 ) is invalid in an SR flip-flop because it leads to an indeterminate state.

</details>

#### 207. When an inverter is placed between both inputs of an SR flip-flop, the resulting flip-flop is:

1. $$\text{JK flip-flop}$$
2. $$\text{T flip-flop}$$
3. $$\text{D flip-flop}$$
4. $$\text{Master-slave JK flip-flop}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$\text{D flip-flop}$$

**Explanation:**

* Placing an inverter between the inputs of an SR flip-flop converts it into a D flip-flop, where the input is directly passed to the output on a clock edge.

</details>

#### 208. The clock signals are used in sequential logic circuits to:

1. $$\text{Tell the time of the day}$$
2. $$\text{Tell how much time has elapsed since the system was turned on}$$
3. $$\text{Carry serial data signals}$$
4. $$\text{Synchronize events in various parts of a system}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{Synchronize events in various parts of a system}$$

**Explanation:**

* Clock signals are used to synchronize the operations of sequential logic circuits, ensuring proper timing and coordination.

</details>

#### 209. What logic function is obtained by adding an inverter to the output of an AND gate?

1. $$\text{OR}$$
2. $$\text{XOR}$$
3. $$\text{NAND}$$
4. $$\text{NOR}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$\text{NAND}$$

**Explanation:**

* Adding an inverter to the output of an AND gate results in a NAND gate, which performs the NOT-AND operation.

</details>

#### 210. The simplified form of the Boolean expression ( (X + Y + XY)(X + Z) ) is:

1. $$X + Y + Z$$
2. $$X + YZ$$
3. $$XY + YZ$$
4. $$XZ + Y$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$X + YZ$$

**Explanation:**

* The expression simplifies to ( X + YZ ) using Boolean algebra rules.

</details>

#### 211. The highest decimal number that can be represented with 10 binary digits is:

1. $$1023$$
2. $$512$$
3. $$1024$$
4. $$2048$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$1023$$

**Explanation:**

* With 10 binary digits, the highest decimal number that can be represented is ( 2^{10} - 1 = 1023 ).

</details>

#### 212. What is the hexadecimal equivalent of the binary number 10101111?

1. $$AF$$
2. $$8C$$
3. $$OF$$
4. $$All of the above$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$AF$$

**Explanation:**

* The binary number 10101111 converts to the hexadecimal number AF.

</details>

#### 213. Which of the following logic families has the highest noise immunity?

1. $$\text{RTL}$$
2. $$\text{TTL}$$
3. $$\text{DTL}$$
4. $$\text{HTL}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{HTL}$$

**Explanation:**

* HTL (High-Threshold Logic) has the highest noise immunity due to its higher voltage levels.

</details>

#### 214. Pick up the wrong logical expression:

1. $$1 + 0 = 0 + 1 = 1$$
2. $$X + Y = X \cdot Y$$
3. $$0 + 0 = 1 \cdot 1 = 0$$
4. $$X + 0 = X$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$X + Y = X \cdot Y$$

**Explanation:**

* The expression ( X + Y = X \cdot Y ) is incorrect because OR and AND operations are not equivalent.

</details>

#### 215. In a four-input NAND gate, all but one input is 1. The output is:

1. $$4$$
2. $$1$$
3. $$0$$
4. $$\text{Undefined}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$0$$

**Explanation:**

* In a NAND gate, if any input is 0, the output is 1. However, if all inputs are 1, the output is 0.

</details>

#### 216. In a four-input AND gate, all but one input is 1. The output is:

1. $$0$$
2. $$1$$
3. $$\text{Undefined}$$
4. $$4$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$0$$

**Explanation:**

* In an AND gate, if any input is 0, the output is 0.

</details>

#### 217. According to the Idempotent law, ( X + X = ):

1. $$1$$
2. $$X$$
3. $$0$$
4. $$X \cdot X$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$X$$

**Explanation:**

* The Idempotent law states that ( X + X = X ).

</details>

#### 218. According to the Idempotent law, ( X \cdot X = ):

1. $$1$$
2. $$X$$
3. $$0$$
4. $$X + X$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$X$$

**Explanation:**

* The Idempotent law states that ( X \cdot X = X ).

</details>

#### 219. The output will be one in case any input is one in the case of:

1. $$\text{OR gate}$$
2. $$\text{NAND gate}$$
3. $$\text{AND gate}$$
4. $$\text{NOT gate}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$\text{OR gate}$$

**Explanation:**

* In an OR gate, the output is 1 if any input is 1.

</details>

#### 220. Which of the following circuits is known as a half adder?

1. $$\text{EXCLUSIVE AND circuit}$$
2. $$\text{INCLUSIVE OR circuit}$$
3. $$\text{Flip-flop circuit}$$
4. $$\text{EXCLUSIVE OR circuit}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{EXCLUSIVE OR circuit}$$

**Explanation:**

* A half adder consists of an XOR gate for the sum and an AND gate for the carry.

</details>

#### 221. Which of the following functions is referred to as the complementary function?

1. $$\text{OR function}$$
2. $$\text{NAND function}$$
3. $$\text{NOT function}$$
4. $$\text{AND function}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$\text{NOT function}$$

**Explanation:**

* The NOT function is the complementary function, as it inverts the input.

</details>

#### 222. Which of the following statements illustrates the distributive law?

1. $$(A + B) + C = A + (B + C) = A + B + C$$
2. $$(A \cdot B) \cdot C = A \cdot (B \cdot C) = A \cdot B \cdot C$$
3. $$A + B = B + A$$
4. $$A \cdot (B + C) = (A \cdot B) + (A \cdot C)$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$A \cdot (B + C) = (A \cdot B) + (A \cdot C)$$

**Explanation:**

* The distributive law states that ( A \cdot (B + C) = (A \cdot B) + (A \cdot C) ).

</details>

#### 223. Which of the following is termed as the minimum error code?

1. $$\text{Binary code}$$
2. $$\text{Excess-3 code}$$
3. $$\text{Gray code}$$
4. $$\text{Octal code}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$\text{Gray code}$$

**Explanation:**

* Gray code is designed to minimize errors in digital communication, as only one bit changes between consecutive values.

</details>

#### 224. For which of the following flip-flops is the output clearly defined for all combinations of two inputs?

1. $$\text{D-type flip-flop}$$
2. $$\text{JK flip-flop}$$
3. $$\text{R-S flip-flop}$$
4. $$\text{T flip-flop}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$\text{JK flip-flop}$$

**Explanation:**

* The JK flip-flop has a defined output for all input combinations, including the toggle state.

</details>

#### 225. A 4-bit shift register can be made by using:

1. $$3 \text{ JK flip-flops}$$
2. $$5 \text{ JK flip-flops}$$
3. $$4 \text{ JK flip-flops}$$
4. $$8 \text{ JK flip-flops}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$4 \text{ JK flip-flops}$$

**Explanation:**

* A 4-bit shift register requires 4 flip-flops, one for each bit.

</details>

#### 226. Which of the following statements is false?

1. $$\overline{A \cdot B} = \overline{A} + \overline{B}$$
2. $$\overline{A + B} = \overline{A} \cdot \overline{B}$$
3. $$A + B = \overline{A} \cdot \overline{B}$$
4. $$A + A = A$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$A + B = \overline{A} \cdot \overline{B}$$

**Explanation:**

* The statement ( A + B = \overline{A} \cdot \overline{B} ) is false according to De Morgan's laws.

</details>

#### 227. The minimum form of the expression ( (A + B)(A + B + C) ) is:

1. $$A + C$$
2. $$A + B$$
3. $$A + B + C$$
4. $$A + BC$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$A + BC$$

**Explanation:**

* The expression simplifies to ( A + BC ) using Boolean algebra.

</details>

#### 228. One's complement of 1011.01 is:

1. $$0100.10$$
2. $$1011.10$$
3. $$0100.11$$
4. $$0100.01$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$0100.10$$

**Explanation:**

* The one's complement is obtained by inverting all the bits.

</details>

#### 229. The NAND gate output will be low if the two inputs are:

1. $$00$$
2. $$10$$
3. $$01$$
4. $$11$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$11$$

**Explanation:**

* A NAND gate outputs 0 only when all inputs are 1.

</details>

#### 230. What is the binary equivalent of the decimal number 368?

1. $$101110000$$
2. $$111010000$$
3. $$110110000$$
4. $$111100000$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$101110000$$

**Explanation:**

* The binary equivalent of 368 is 101110000.

</details>

#### 231. The decimal equivalent of the hexadecimal number 1A53 is:

1. $$6793$$
2. $$6973$$
3. $$6739$$
4. $$6379$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$6793$$

**Explanation:**

* The hexadecimal number 1A53 converts to the decimal number 6793.

</details>

#### 232. The octal equivalent of the decimal number 324.987 is:

1. $$504.771$$
2. $$815.234$$
3. $$640.781$$
4. $$90.987$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$504.771$$

**Explanation:**

* The decimal number 324.987 converts to the octal number 504.771.

</details>

#### 233. The simplification of the Boolean expression ( (A \cdot B \cdot C) + (A \cdot B \cdot \overline{C}) ) is:

1. $$0$$
2. $$A$$
3. $$A \cdot B$$
4. $$B \cdot C$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$A \cdot B$$

**Explanation:**

* The expression simplifies to ( A \cdot B ) using Boolean algebra.

</details>

#### 234. The number of control lines for an 8-to-1 multiplexer is:

1. $$2$$
2. $$4$$
3. $$3$$
4. $$5$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$3$$

**Explanation:**

* An 8-to-1 multiplexer requires 3 control lines (since ( 2^3 = 8 )).

</details>

#### 235. How many flip-flops are required for a mod-16 counter?

1. $$5$$
2. $$3$$
3. $$4$$
4. $$6$$

<details>

<summary>Show me the answer</summary>

**Answer:** 3. $$4$$

**Explanation:**

* A mod-16 counter requires 4 flip-flops (since ( 2^4 = 16 )).

</details>

#### 236. EPROM contents can be erased by exposing it to:

1. $$\text{Ultraviolet light}$$
2. $$\text{Burst of microwaves}$$
3. $$\text{Infrared rays}$$
4. $$\text{Intense heat radiations}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$\text{Ultraviolet light}$$

**Explanation:**

* EPROMs are erased by exposing them to ultraviolet light.

</details>

#### 237. The hexadecimal number 'A0' has the decimal value equivalent to:

1. $$80$$
2. $$100$$
3. $$256$$
4. $$160$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$160$$

**Explanation:**

* The hexadecimal number A0 converts to the decimal number 160.

</details>

#### 238. The Gray code for decimal number 6 is equivalent to:

1. $$1100$$
2. $$0101$$
3. $$1001$$
4. $$0110$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$0110$$

**Explanation:**

* The Gray code for decimal 6 is 0110.

</details>

#### 239. The Boolean expression ( A \cdot B + A \cdot \overline{B} + \overline{A} \cdot B ) is equivalent to:

1. $$A + B$$
2. $$A \cdot B$$
3. $$\overline{A} + \overline{B}$$
4. $$A \oplus B$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$A + B$$

**Explanation:**

* The expression simplifies to ( A + B ) using Boolean algebra.

</details>

#### 240. The 2's complement of the binary number 1101101 is:

1. $$0010011$$
2. $$0010010$$
3. $$0010001$$
4. $$0010000$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$0010011$$

**Explanation:**

* The 2's complement of 1101101 is 0010011.

</details>

#### 241. The digital logic family which has minimum power dissipation is:

1. $$\text{TTL}$$
2. $$\text{DTL}$$
3. $$\text{RTL}$$
4. $$\text{CMOS}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{CMOS}$$

**Explanation:**

* CMOS logic has the lowest power dissipation among the given options.

</details>

#### 242. The output of a logic gate is 1 when all its inputs are at logic 0. The gate is either:

1. $$\text{NAND or EX-OR}$$
2. $$\text{AND or EX-OR}$$
3. $$\text{OR or EX-NOR}$$
4. $$\text{NOR or EX-NOR}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{NOR or EX-NOR}$$

**Explanation:**

* A NOR gate outputs 1 when all inputs are 0, and an EX-NOR gate outputs 1 when all inputs are equal.

</details>

#### 243. Data can be changed from special code to temporal code by using:

1. $$\text{Shift registers}$$
2. $$\text{Combinational circuits}$$
3. $$\text{Counters}$$
4. $$\text{Multiplexers}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$\text{Shift registers}$$

**Explanation:**

* Shift registers are used to convert data from parallel to serial form or vice versa.

</details>

#### 244. A ring counter consisting of five flip-flops will have:

1. $$5 \text{ states}$$
2. $$32 \text{ states}$$
3. $$10 \text{ states}$$
4. $$\text{Infinite states}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$5 \text{ states}$$

**Explanation:**

* A ring counter with 5 flip-flops has 5 unique states.

</details>

#### 245. The speed of conversion is maximum in:

1. $$\text{Successive-approximation A/D converter}$$
2. $$\text{Parallel-comparator A/D converter}$$
3. $$\text{Counter-ramp A/D converter}$$
4. $$\text{Dual-slope A/D converter}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$\text{Parallel-comparator A/D converter}$$

**Explanation:**

* Parallel-comparator A/D converters have the fastest conversion speed.

</details>

#### 246. The 2's complement of the number 1101101 is:

1. $$0010011$$
2. $$0010010$$
3. $$0010001$$
4. $$0010000$$

<details>

<summary>Show me the answer</summary>

**Answer:** 1. $$0010011$$

**Explanation:**

* The 2's complement of 1101101 is 0010011.

</details>

#### 247. The correction to be applied in a decimal adder to the generated sum is:

1. $$A + B$$
2. $$A \cdot B$$
3. $$\overline{A} + \overline{B}$$
4. $$\overline{A} \cdot \overline{B}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$A \cdot B$$

**Explanation:**

* The correction term in a decimal adder is ( A \cdot B ).

</details>

#### 248. When simplified with Boolean algebra, ( (x + y)(x + z) ) simplifies to:

1. $$x$$
2. $$x + yz$$
3. $$x + y + z$$
4. $$x(y + z)$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$x + yz$$

**Explanation:**

* The expression simplifies to ( x + yz ) using Boolean algebra.

</details>

#### 249. The gates required to build a half adder are:

1. $$\text{EX-OR gate and NOR gate}$$
2. $$\text{EX-OR gate and AND gate}$$
3. $$\text{EX-OR gate and OR gate}$$
4. $$\text{Four NAND gates}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 2. $$\text{EX-OR gate and AND gate}$$

**Explanation:**

* A half adder consists of an EX-OR gate for the sum and an AND gate for the carry.

</details>

#### 250. The code where all successive numbers differ from their preceding number by a single bit is:

1. $$\text{Binary code}$$
2. $$\text{Excess-3 code}$$
3. $$\text{BCD code}$$
4. $$\text{Gray code}$$

<details>

<summary>Show me the answer</summary>

**Answer:** 4. $$\text{Gray code}$$

**Explanation:**

* Gray code ensures that only one bit changes between consecutive numbers.

</details>