Among the nitrates of alkali metals,which one can be decomposed to its oxide on strong heating?

As the mass number $A$ increases,which of the following quantities related to the nucleus does not change?

Two charges $+3.2 \times 10^{-19} \, C$ and $-3.2 \times 10^{-19} \, C$ kept $2.4 \, \mathring{A}$ apart form a dipole. If it is placed in a uniform electric field of intensity $4 \times 10^5 \, V/m$,what will be its potential energy in stable equilibrium?

Compound $B$ is ?

$15 \text{ mL}$ of aqueous solution of $Fe^{2+}$ in acidic medium completely reacted with $20 \text{ mL}$ of $0.03 \text{ M}$ aqueous $Cr_2O_7^{2-}$. The molarity of the $Fe^{2+}$ solution is $\times 10^{-2} \text{ M}$ (Round off to the Nearest Integer).