According to the formula, if a person can do $\frac{1}{x}$^th work in 1 days, then his efficency in percentage is $\frac{100}{\mathrm{x}}\%$.

Similarly here, Ravi can complete $\frac{1}{5}$^th of an assignment in 1 day.

So, his efficiency in percentage is $\frac{100}{5}=20\%$

Hence option B is correct