Question

Which among the following can never be the units digit of a perfect square number?

• A. $4$
• B. $9$
• C. $7$
• D. $6$

Answer 1

The correct option is C $7$

The units digit of a number's square is totally determined by the number's $\underset{–}{\text{units digit}}.$

$\underset{–}{\text{Method to Find the Number's Square Unit Digit.}}$
Stept 1:
The units digit of the number will be squared.

Step 2:
The units digit of this square will be the units digit of the full number's square.

Let's list all the possible unit digits of square numbers:

As per the above table, we observe that the perfect square numbers end with units digit as $0,1,4,5,6$ and $9$ only.

We can say that perfect square numbers don't end with units digit as $2,3,7$ and $8$.

$\therefore 2,3,7$ and $8$ can never be the units digit of a perfect square number.

Therefore, option (c.) is the correct answer.