The dibromo compound $[\mathrm{P}]$ (molecular formula: $\mathrm{C}_9 \mathrm{H}_{10} \mathrm{Br}_2$ ) when heated with excess sodamide followed by treatment with dilute HCl gives [Q]. On warming [Q] with mercuric sulphate and dilute sulphuric acid yield $[R]$ which gives positive Iodoform test but negative Tollen's test. The compound $[\mathrm{P}]$ is :

Which of the following mixture gives a buffer solution with $\mathrm{pH}=9.25$ ?

Given : $\mathrm{pK}_{\mathrm{b}}\left(\mathrm{NH}_4 \mathrm{OH}\right)=4.75$

When 1 g of compound $(\mathrm{X})$ is subjected to Kjeldahl's method for estimation of nitrogen, 15 mL 1 M $\mathrm{H}_2 \mathrm{SO}_4$ was neutralized by ammonia evolved. The percentage of nitrogen in compound $(\mathrm{X})$ is :

The energy of first (lowest) Balmer line of H atom is $x \mathrm{~J}$. The energy (in J) of second Balmer line of H atom is :