How do you explain the presence of five $-$OH groups in glucose molecule?
Glucose on reaction with acetic anhydride produces glucose pentaacetate.
This reaction explain presence of five $-$OH groups.
Why does compound (A) given below not form an oxime?
Compound (A) does not form an oxime on reaction with NH$_2$OH due to absence of CHO group 
group.
Why must vitamin $C$ be supplied regularly in diet?
Vitamin C is water soluble hence, they are regularly excreted in urine and can not be stored in our body, so, they are supplied regularly in diet.
Sucrose is dextrorotatory but the mixture obtained after hydrolysis is laevorotatory. Explain.
Sucrose is dextrorotatory. On hydrolysis, it produces a mixture of glucose and fructose having specific rotation $+52.5^{\circ}$ and $-92.4^{\circ}$. Thus, the respectively net resultant mixture become laevorotatory. Hence, the mixture is laevorotatory and product is known as invert sugar.
Amino acids behave like salts rather than simple amines or carboxylic acids. Explain.
Amino acids have acidic COOH group as well as $\mathrm{NH}_2$ group hence, COOH looses its H to $\mathrm{NH}_2$, hence they exist as Z witter ion.
