Among the following, number of metal/s which can be used as electrodes in the photoelectric cell is _________. (Integer answer)

(A) Li

(B) Na

(C) Rb

(D) Cs

The shortest distance between the line x $$-$$ y = 1 and the curve x² = 2y is :

A function f(x) is given by $$f(x) = {{{5^x}} \over {{5^x} + 5}}$$, then the sum of the series $$f\left( {{1 \over {20}}} \right) + f\left( {{2 \over {20}}} \right) + f\left( {{3 \over {20}}} \right) + ....... + f\left( {{{39} \over {20}}} \right)$$ is equal to :

Let x denote the total number of one-one functions from a set A with 3 elements to a set B with 5 elements and y denote the total number of one-one functions form the set A to the set A $$\times$$ B. Then :