Which one of the following cell organelles is enclosed by a single membrane?

Zirconium phosphate $[Zr_3(PO_4)_4]$ dissociates into three zirconium cations of charge $+4$ and four phosphate anions of charge $-3$. If molar solubility of zirconium phosphate is denoted by $S$ and its solubility product by $K_{sp}$,then which of the following relationships between $S$ and $K_{sp}$ is correct?

Widal test is used for the diagnosis of

The oxidation number of $C$ in $HNC$ is .......

The focal length of a convex lens will be maximum for:

The number of $p\pi-d\pi$ 'pi' bonds present in $XeO_3$ and $XeO_4$ molecules,respectively,are: