The correct sequence of reagents for the preparation of Q  and R is: 

The conversion of n-heptane into benzoic acid and benzyl alcohol proceeds through aromatization, controlled oxidation, disproportionation, and acidification.

n-Heptane undergoes cyclization and dehydrogenation in the presence of chromium oxide at high temperature and pressure to form toluene:

$$\mathrm{C_7H_{16} \xrightarrow[20\,atm]{Cr_2O_3,\;770\,K} C_6H_5CH_3}$$

Toluene is then subjected to Étard oxidation using chromyl chloride followed by hydrolysis to give benzaldehyde:

$$\mathrm{C_6H_5CH_3 \xrightarrow{CrO_2Cl_2,\;H_3O^+} C_6H_5CHO}$$

Benzaldehyde contains no α-hydrogen and therefore undergoes the Cannizzaro reaction with concentrated sodium hydroxide:

$$\mathrm{2C_6H_5CHO + NaOH \rightarrow C_6H_5CH_2OH + C_6H_5COONa}$$

The sodium benzoate formed is acidified to obtain benzoic acid:

$$\mathrm{C_6H_5COONa + H_3O^+ \rightarrow C_6H_5COOH + Na^+ + H_2O}$$

Thus,

$$Q = \mathrm{C_6H_5COOH}$$

$$R = \mathrm{C_6H_5CH_2OH}$$

Hence, the correct sequence of reagents is

$$\boxed{(i)\ Cr_2O_3,\ 770\,K,\ 20\,atm \;\rightarrow\; (ii)\ CrO_2Cl_2,\ H_3O^+ \;\rightarrow\; (iii)\ NaOH \;\rightarrow\; (iv)\ H_3O^+}$$

Therefore, the correct answer is $$\boxed{\text{Option A}}$$.