Question

answer this question

Answer 1

option B is right answer

Let length of its side be x

by Pythagoras theorem,

x²+x²=10²

2x²=100

x²=50

x=√50

or x=5√2

Answer 2

Here is your answer
Let the side of a square is X
so Diagonal*2 = X*2 +X*2
$(10) {}^{2} = 2x {}^{2} \\ x {}^{2} = 100 \div 2 \\ x = \sqrt{100 \div 2 } \\ x = 10 \div \sqrt{2} \\ x = 5 \sqrt{2} cm$
Hope it helps you