$$20 \mathrm{~mL}$$ of $$0.1\, \mathrm{M} \,\mathrm{NH}_{4} \mathrm{OH}$$ is mixed with $$40 \mathrm{~mL}$$ of $$0.05 \mathrm{M} \mathrm{HCl}$$. The $$\mathrm{pH}$$ of the mixture is nearest to :

(Given : $$\mathrm{K}_{\mathrm{b}}\left(\mathrm{NH}_{4} \mathrm{OH}\right)=1 \times 10^{-5}, \log 2=0.30, \log 3=0.48, \log 5=0.69, \log 7=0.84, \log 11= 1.04)$$

The IUPAC nomenclature of an element with electronic configuration [Rn] $$5 \mathrm{f}^{14} 6 \mathrm{d}^{1} 7 \mathrm{s}^{2}$$ is :

A compound ‘$$\mathrm{A}$$’ on reaction with ‘$$\mathrm{X}$$’ and ‘$$\mathrm{Y}$$’ produces the same major product but different by product '$$a$$' and '$$b^{\prime}$$. Oxidation of '$$a$$' gives a substance produced by ants.

'X' and 'Y' respectively are

Most stable product of the following reaction is: