How many significant digits are present in the value of $\sqrt{6.5-6.32}$ ?

$\sqrt{6.5-6.32}=\sqrt{6.5-6.3}=\sqrt{0.2}=0.447214=0.4$

(The number of significant figures in multiplication or division should equal to minimum number of decimal points of a quantity involved in the operation.)

Thus, number of significant digit in 0.4 is 1.