TN State Board 12th Chemistry Question Paper 2022

Elements in group 15 have the valence shell configuration $ns^2 np^3$. The 3rd period indicates the principal quantum number $n=3$. Therefore, the valence shell configuration is $3s^2 3p^3$. Adding the core electrons ($1s^2 2s^2 2p^6$), the full configuration is $1s^2 2s^2 2p^6 3s^2 3p^3$. Choice (A) corresponds to Silicon (Group 14), (B) is Oxygen (Period 2), and (D) is Nitrogen (Period 2).

Bauxite is the principal ore of aluminium and is represented by the formula $Al_2O_3 \cdot nH_2O$. It typically contains varying amounts of water. $Al_2O_3$ (anhydrous) is Corundum, and $Fe_2O_3 \cdot nH_2O$ is Limonite.

For a first-order reaction, the rate constant $k = \frac{2.303}{t} \log(\frac{[A]_0}{[A]_t})$. When 75% is completed, $[A]_t = 0.25[A]_0$, so $k = \frac{2.303}{60} \log(4) = \frac{2.303}{60} \times 0.602$. The half-life $t_{1/2} = \frac{0.693}{k}$. Substituting $k$, we get $t_{1/2} = \frac{0.693 \times 60}{2.303 \times 0.602} \approx 30$ minutes.

Nitrobenzene can be reduced to aniline (amino benzene) using metal-acid combinations like $Sn/HCl$, $Fe/HCl$, or $Zn/HCl$ (catalytic hydrogenation is also possible). $Sn/HCl$ is the standard laboratory method. $Zn/NH_4Cl$ is typically used to stop at the intermediate phenylhydroxylamine stage, and $ZnHg/NaOH$ is a Clemmensen reduction condition usually reserved for carbonyls.

Periodic acid ($HIO_4$) cleaves 1,2-diols (vicinal diols) at the C-C bond. For ethylene glycol ($HO-CH_2-CH_2-OH$), the cleavage results in two molecules of formaldehyde ($CH_2O$ or methanal).