What is the smallest $4$ digit number ?

1. 1000

The correct option is A 1000
For the smallest $4$ digit number, we use the smallest possible digit at all places .

Bur $0000$ = $0$, which is not a four digit number.

We have to use a smallest non-zero digit at $1000$s place. Smallest non zero digit is $1$

Thus, smallest $4$ digit number is $1000$