Which of the following contains both ionic and covalent bonds?

The correct match of the group reagents in List$-I$ for precipitating the metal ion given in List$-II$ from solutions, is

List$-I$	List$-II$
$(P)$ Passing $H _2 S$ in the presence of $NH _4 OH$	$(1) \ Cu ^{2+}$
$(Q) \ \left( NH _4\right)_2 CO _3$ in the presence of $NH _4 OH$	$(2) \ Al ^{3+}$
$(R) \ NH _4 OH$ in the presence of $NH _4 Cl$	$(3) \ Mn ^{2+}$
$(S)$ Passing $H _2 S$ in the presence of dilute $\text{HCl}$	$(4) \ Ba ^{2+}$
	$(5) \ Mg ^{2+}$

Green glands,present in some arthropods,help in

When a current of $2\,A$ flows in a battery from negative to positive terminal,the potential difference across it is $12\,V$. If a current of $3\,A$ flows in the opposite direction,the potential difference across the terminals of the battery is $15\,V$. The emf of the battery is ............... $V$.

$A$ particle of mass $M$ is moving in a horizontal circle of radius $R$ with uniform speed $V$. When it moves from one point to a diametrically opposite point,its

Methanogens belong to $..........$.