Assertion :- The backbone of polynucleotide chain is formed due to sugar and phosphate.
Reason :- A nitrogenous base is linked to the pantose sugar through a N-glycosidic linkage to formed a nucleoside.

Options

A. If both Assertion & Reason are True & the Reason is a correct explanation of the Assertion.
B. If both Assertion & Reason are True but Reason is not a correct explanation of the Assertion.
C. If Assertion is True but the Reason is False.
D. If both Assertion & Reason are False.

Answer

**Step-by-Step Solution:**

1. **Understanding the Assertion:**
- The assertion states that the backbone of a polynucleotide chain is formed due to sugar and phosphate.
- In a polynucleotide, which is a polymer made up of many nucleotides, the sugar (pentose sugar) and phosphate groups alternate to form the backbone.

2. **Defining Nucleotide:**
- A nucleotide consists of three components: a pentose sugar, a nitrogenous base, and a phosphate group.
- The pentose sugar can be either ribose (in RNA) or deoxyribose (in DNA).

3. **Structure of Nucleotide:**
- In a nucleotide, the pentose sugar is connected to a nitrogenous base at the 1' carbon (C1) through a glycosidic bond.
- The phosphate group is attached to the 5' carbon (C5) of the sugar.

4. **Understanding the Reason:**
- The reason states that a nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside.
- This statement is correct because the bond between the nitrogenous base and the sugar is indeed an N-glycosidic bond, forming a nucleoside when the phosphate group is not included.

5. **Conclusion:**
- Both the assertion and the reason are true. However, the reason does not provide a correct explanation for the assertion. The assertion focuses on the backbone structure of the polynucleotide, while the reason describes the formation of a nucleoside.

**Final Answer:**
- The correct option is that both the assertion (A) and the reason (R) are true, but R is not the correct explanation for A.

---