Which of the following is a natural polymer?

The origin is translated to $(1,2)$. The point $(7,5)$ in the old system undergoes the following transformations successively.
$I$. Moves to the new point under the given translation of origin.
$II$. Translated through $2$ units along the negative direction of the new $X$-axis.
$III$. Rotated through an angle $\frac{\pi}{4}$ about the origin of the new system in the clockwise direction. The final position of the point $(7,5)$ is

Which of the following is an unsuitable habitat for algae?

The $pK_a$ values of four carboxylic acids are $4.76, 4.19, 0.23$,and $3.41$ respectively. The $pK_a$ value of the strongest carboxylic acid among them is

The logical statement $(\sim(\sim p \vee q) \vee(p \wedge r)) \wedge(\sim q \wedge r)$ is equivalent to

In which of the following reactions does hydrogen act as an oxidizing agent?