(a) Glucose with nitric acid

Concentrated nitric acid is a strong oxidising agent. It oxidises both terminal groups of glucose — the aldehyde at C-1 and the primary alcohol at C-6 — into carboxyl groups :

$$\underset{\text{glucose}}{CHO-(CHOH)_4-CH_2OH} \xrightarrow{\text{conc. }HNO_3} \underset{\text{saccharic acid}}{COOH-(CHOH)_4-COOH}$$

Product : saccharic acid (also called glucaric acid), a dicarboxylic acid.

What this proves : glucose contains one aldehyde group and one primary alcoholic group, situated at the two ends of the carbon chain.

Useful contrast : the milder oxidising agent bromine water attacks only the $-CHO$ group, giving gluconic acid and leaving the $-CH_2OH$ intact. Comparing the two products is how the positions of the groups were established.

(b) One structural difference between DNA and RNA

The pentose sugar is different.

DNA contains $\beta$-D-2-deoxyribose, in which the $-OH$ group at C-2 has been replaced by a hydrogen atom.

RNA contains $\beta$-D-ribose, which retains the $-OH$ group at C-2.

(Another acceptable difference : DNA contains the base thymine whereas RNA contains uracil; or DNA is double-stranded and helical while RNA is usually single-stranded.)