Electric field at a point varies as $r^0$ for

The figure shows the variation of photocurrent with anode potential for a photo-sensitive surface for three different radiations. Let $I_a, I_b$ and $I_c$ be the intensities and $f_a, f_b$ and $f_c$ be the frequencies for the curves $a, b$ and $c$ respectively.

$A$ car is moving along a straight line,say $OP$ in the given figure. It moves from $O$ to $P$ in $18 \; s$ and returns from $P$ to $Q$ in $6.0 \; s$. What are the average velocity and average speed of the car in going from $O$ to $P$?

From the ground state electronic configuration of the elements given below,pick the one with the highest value of second ionisation energy.

Consider two statements $S_1$ and $S_2$.
$S_1$: If $f(x)$ is a differentiable function with $f'(x) = 0$ in $(a, b)$ and $f(x)$ is increasing in $(a, b)$,then $\frac{f(x)}{f'(x)}$ is also increasing in $(a, b)$.
$S_2$: Both $\sin x$ and $\tan x$ are increasing functions in $(0, \frac{\pi}{2})$.
Which of the following is true?

If the slope of one line is twice the slope of the other in the pair of straight lines $ax^2 + 2hxy + by^2 = 0$,then $8h^2$ is equal to (in $ab$)