Cyclohexylamine when treated with nitrous acid yields $(\mathrm{P})$. On treating $(\mathrm{P})$ with $\mathrm{PCC}$ results in (Q). When $(\mathrm{Q})$ is heated with dil. $\mathrm{NaOH}$ we get $(\mathrm{R})$ The final product (R) is :

Compound $\mathrm{A}, \mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{5}$, given a tetraacetate with $\mathrm{Ac}_{2} \mathrm{O}$ and oxidation of $\mathrm{A}$ with $\mathrm{Br}_{2}-\mathrm{H}_{2} \mathrm{O}$ gives an acid, $\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O}_{6}$. Reduction of $\mathrm{A}$ with $\mathrm{HI}$ gives isopentane. The possible structure of $\mathrm{A}$ is

An organic compound $[\mathrm{A}]\left(\mathrm{C}_{4} \mathrm{H}_{11} \mathrm{~N}\right)$, shows optical activity and gives $\mathrm{N}_{2}$ gas on treatment with $\mathrm{HNO}_{2}$. The compound $[\mathrm{A}]$ reacts with $\mathrm{PhSO}_{2} \mathrm{Cl}$ producing a compound which is soluble in $\mathrm{KOH}$. The structure of $\mathrm{A}$ is :

Which of the following elements have half-filled f-orbitals in their ground state?

(Given : atomic number $\mathrm{Sm}=62 ; \mathrm{Eu}=63 ; \mathrm{Tb}=65 ; \mathrm{Gd}=64, \mathrm{Pm}=61$ )

A. $\mathrm{Sm}$

B. Eu

C. $\mathrm{Tb}$

D. Gd

E. $\mathrm{Pm}$

Choose the correct answer from the options given below :