• Basic Structural Unit of Carbohydrates:
• Monosaccharides (simple sugars such as glucose, fructose, and galactose) are the fundamental monomeric units of carbohydrates with the empirical formula $(CH_2O)_n$.
• They cannot be hydrolyzed into simpler carbohydrate molecules and serve as the building blocks for disaccharides, oligosaccharides, and polysaccharides.

Correct option: (2) Monosaccharide

• Chirality of Amino Acids:
• In 19 of the 20 standard proteinogenic amino acids, the central $\alpha$-carbon is covalently bound to four different chemical substituents: $-\text{COOH}$, $-\text{NH}_2$, $-\text{H}$, and a variable side chain ($-\text{R}$). This makes the $\alpha$-carbon an asymmetric (chiral) center.
• In Glycine, the side chain is simply a hydrogen atom ($-\text{H}$). Because the $\alpha$-carbon is bound to two identical hydrogen atoms, it has no chiral center and is optically inactive.

Correct option: (3) Glycin

Evaluating the Assertion and Reason concerning Light signaling in plants:

The correct answer is Option 1: Both (A) and (R) are correct and (R) is the correct explanation of (A)..