Which of the following substances undergoes sublimation?

The cathode of a photoelectric cell is changed from a work function $W_1$ to $W_2$ $(W_2 > W_1)$. If the photoelectric currents before and after the change are $I_1$ and $I_2$ respectively,and all other conditions remain constant,then which of the following is true? (Assume $hv > W_2$)

Let $PQ$ and $RS$ be tangents at the extremities of the diameter $PR$ of a circle of radius $r$. If $PS$ and $RQ$ intersect at a point $X$ on the circumference of the circle,then $2r$ equals

Yeast is used in the production of

Which one of the following represents the graph between $\log p$ (on $Y$-axis) and $\frac{1}{T}$ (on $X$-axis)?
($p=$ vapour pressure of a liquid,$T=$ absolute temperature)

Which of the following groups of transition metals are known as coinage metals?