(A) Oxidation of 1^o alcohols with anhydrous ${\mathrm{CrO}}_3$ will gives aldehydes but not carboxylic    acids 

(R) Anhydrous ${\mathrm{CrO}}_3$ is a mild oxidant

Aldehydes are produced by oxidizing primary alcohols. Carboxylic acids are generated by further oxidizing aldehydes.

Chromium trioxide is a potent oxidizing agent that tends to explode when in contact with organic compounds and solvents. It is not soluble in the majority of organic solvents.

Hence, Option A is correct.