n is a whole number which when divided by 4 gives 3 as remainder. what will be the remainder when 2n is divided by 4 ?

The remainder will be 2.

Quick reasoning

Let the whole number be nnn.
You’re told that when nnn is divided by 4, the remainder is 3.
That means we can write:

n=4k+3n=4k+3n=4k+3

for some whole number kkk. Now double it:

2n=2(4k+3)=8k+62n=2(4k+3)=8k+62n=2(4k+3)=8k+6

Divide 2n2n2n by 4:

2n=8k+6=4(2k+1)+22n=8k+6=4(2k+1)+22n=8k+6=4(2k+1)+2

So when 2n2n2n is divided by 4, the remainder is 2.