Which of the following hydroxides is acidic?

Which of the following theories provides the latest explanation for the closure of stomata?

If $a = \frac{1-i \sqrt{3}}{2}$,then the correct matching of List-$I$ with List-$II$ is:

List-$I$	List-$II$
$(i) \ a \bar{a}$	$(A) -\frac{\pi}{3}$
$(ii) \ \arg \left(\frac{1}{\bar{a}}\right)$	$(B) -i \sqrt{3}$
$(iii) \ a-\bar{a}$	$(C) \frac{2i}{\sqrt{3}}$
$(iv) \ \operatorname{Im}\left(\frac{4}{3a}\right)$	$(D) 1$
	$(E) \frac{\pi}{3}$
	$(F) \frac{2}{\sqrt{3}}$

$Na_2S + Na_2[Fe(CN)_5NO] \longrightarrow Na_4[Fe(CN)_5NOS]$; what are the oxidation numbers of $Fe$ in the reactant complex and the product complex,respectively?

$\cos ^2\left(\frac{\pi}{6}+\theta\right)-\sin ^2\left(\frac{\pi}{6}-\theta\right)$ is equal to

Two circles whose radii are equal to $4$ and $8$ intersect at right angles. The length of their common chord is