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 contrapositive of the statement "If you will work, you will earn money" is :

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

A plane passes through the points A(1, 2, 3), B(2, 3, 1) and C(2, 4, 2). If O is the origin and P is (2, $$-$$1, 1), then the projection of $$\overrightarrow {OP} $$ on this plane is of length :