Question

If num is an int which expression always evaluates to true if num holds an odd number

Answer 1

The answer is 2) Num%2==1.
The modulus operator (%) divides the left hand side by the right hand side and returns the remainder.

Examples:
3%2=1 : 2 goes into 3 once, with 1 remaining.

5%2 =1 :  2 goes into 5 twice, with 1 remaining.

11%2 =1 :  2 goes into 11 five times, with 1 remaining.