Go through the following statements:
(i) In RNA the uracil is found in place of 5-methyl uracil
(ii) A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside
(iii) Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.
(iv). The length of double DNA helix in a typical mammalian cell is approximately 3.2 metres.
find out the correct statement

Options

A. (i), (ii), & (iii)
B. All are correct
C. (ii) & (iii)
D. (ii), (iii) & (iv)

Explanation

To determine the correct statements from the given options, let's analyze each statement step by step.

### Step 1: Analyze Statement (i)
**Statement:** In RNA, uracil is found in place of 5-methyl uracil.

**Analysis:**
- In RNA, the nitrogenous base uracil (U) is indeed present instead of thymine (T), which is found in DNA.
- 5-methyl uracil is another name for thymine, which has a methyl group that uracil lacks.
- Therefore, this statement is **correct**.

### Step 2: Analyze Statement (ii)
**Statement:** A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside.

**Analysis:**
- A nucleoside is formed when a nitrogenous base (adenine, guanine, cytosine, or uracil) is attached to a pentose sugar (ribose in RNA or deoxyribose in DNA) via an N-glycosidic bond.
- This statement accurately describes the formation of a nucleoside, so it is **correct**.

### Step 3: Analyze Statement (iii)
**Statement:** Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.

**Analysis:**
- Nucleotides are indeed linked together by phosphodiester bonds, which connect the 3' carbon of one nucleotide's sugar to the 5' phosphate group of another nucleotide's sugar.
- This statement correctly describes the formation of a dinucleotide, so it is **correct**.

### Step 4: Analyze Statement (iv)
**Statement:** The length of double DNA helix in a typical mammalian cell is approximately 3.2 meters.

**Analysis:**
- The total length of DNA in a typical mammalian cell is approximately 2.2 meters, not 3.2 meters.
- Therefore, this statement is **incorrect**.

### Conclusion
The correct statements are:
- (i) In RNA, uracil is found in place of 5-methyl uracil.
- (ii) A nitrogenous base is linked to the pentose sugar through an N-glycosidic linkage to form a nucleoside.
- (iii) Two nucleotides are linked through 3'-5' phosphodiester linkage to form a dinucleotide.

Thus, the correct answer is **Statements (i), (ii), and (iii) are correct**.

---