# ISRO Core CS Questions with Answers

8 previously-asked core cs questions from ISRO's hiring process, each with the correct answer and a worked explanation. Written against the company's actual test pattern.

_Source: Astra (https://useastra.in). Updated 2026-09-05._

### 1. What is the decimal value of the binary number 1010?

A. 10
B. 12
C. 8
D. 6

**Answer:** 10

**Explanation:** 1010 in binary is 8 + 2 = 10.

### 2. Which sorting algorithm has O(n log n) time in the worst case?

A. Merge sort
B. Bubble sort
C. Selection sort
D. Insertion sort

**Answer:** Merge sort

**Explanation:** Merge sort is O(n log n) in all cases; the others are O(n^2) in the worst case.

### 3. Which of the following is NOT a necessary condition for deadlock?

A. Mutual exclusion
B. Hold and wait
C. Preemption
D. Circular wait

**Answer:** Preemption

**Explanation:** The four conditions are mutual exclusion, hold and wait, no preemption, and circular wait; allowing preemption prevents deadlock.

### 4. Which statement about TCP is correct?

A. It is connection oriented and reliable
B. It is connectionless
C. It does not guarantee ordering
D. It has no error checking

**Answer:** It is connection oriented and reliable

**Explanation:** TCP establishes a connection and provides reliable, ordered delivery.

### 5. What is the time complexity of binary search on a sorted array?

A. O(log n)
B. O(n)
C. O(1)
D. O(n^2)

**Answer:** O(log n)

**Explanation:** Binary search halves the search range each step, giving logarithmic time.

### 6. Which data structure follows Last In First Out order?

A. Stack
B. Queue
C. Array
D. Graph

**Answer:** Stack

**Explanation:** A stack removes the most recently added element first, which is LIFO.

### 7. What is the result of the Boolean expression A OR 1?

A. 1
B. 0
C. A
D. NOT A

**Answer:** 1

**Explanation:** ORing anything with 1 always gives 1.

### 8. What is the value of 2 raised to the power 8?

A. 256
B. 128
C. 512
D. 64

**Answer:** 256

**Explanation:** 2 to the 8 equals 256.

More ISRO preparation, including the full recruitment process: https://useastra.in/campus/isro