Identify the substrate 'A' in the following reaction.
$\text{A} \xrightarrow[\large{\text{ii)}\ \Delta}]{\large{\text{i) Moist Ag}_2\text{O}}} \text{CH}_3\text{CH}_2\text{N(CH}_3)_2 + \text{CH}_2 = \text{CH}_2$

Which from following amino acids is an essential amino acid ?

Identify a natural source of ascorbic acid from following.

What type of glycosidic bond is present in maltose?