One good way is to express your number as a fraction, and then "count the number of $\frac{1}{16}'s$.
Here, it would give $0.25=\frac{1}{4}=4\times\frac{1}{16}$
And this is true for any number that admits a finite hexadecimal expression : you make it a fraction, with a power of 16 at the denominator, then separate your fraction in chunks with nominator a integer between 0 and 15, and denominator a power of 16. Then the nominators give the hexadecimal decomposition.
Hence,Option(C)0.40 is the correct chocie