Question

A number becomes a perfect square when we subtract $1$ from it. Which of the given options cannot be the last digit of that number?

• A. $2$
• B. $4$
• C. $5$
• D. $0$

Answer 1

The correct option is B

$4$

Step 1: Explanation of the correct option

Given that a number becomes a perfect square when we subtract $1$ from it.

We know that the unit digit of the square numbers will have $0,1,4,5,6,9$.

Thus, for all perfect squares, the unit digit will consist of only $0,1,4,5,6,9$ and none of the square numbers will end with $2,3,7,8$.

According to the question, a number becomes a perfect square when we subtract $1$ from it. Therefore the number's unit's digit cannot be $3,4,8,9$.

Therefore, option (B) is correct.

Step 2: Explanation of the incorrect option

Options (A), (C), and (D) do not give the correct answer.