Analysis:

To determine the length of the DNA fragment, we need to understand the relationship between the number of hydrogen bonds and the number of base pairs in a DNA double helix.

Number of Hydrogen Bonds:
In a DNA double helix, the base pairs are held together by hydrogen bonds. Specifically, adenine (A) pairs with thymine (T) through two hydrogen bonds, while guanine (G) pairs with cytosine (C) through three hydrogen bonds.

Given that there are 23 guanine bases, we can calculate the number of hydrogen bonds as follows:

Number of Hydrogen Bonds = Number of Guanine Bases * 3

Number of Hydrogen Bonds = 23 * 3 = 69

However, we are given that there are 135 hydrogen bonds in the DNA fragment. This indicates that there are additional base pairs in the fragment.

Number of Base Pairs:
Each base pair consists of one purine (adenine or guanine) and one pyrimidine (thymine or cytosine). In a DNA double helix, the number of purine bases is equal to the number of pyrimidine bases.

Since there are 23 guanine bases, there must be an equal number of cytosine bases. Therefore, the total number of base pairs can be calculated as follows:

Number of Base Pairs = Number of Guanine Bases + Number of Cytosine Bases

Number of Base Pairs = 23 + 23 = 46

Now, we can calculate the length of the DNA fragment using the relationship between the number of base pairs and the length of each base pair.

Length of DNA Fragment:
The length of each base pair in a DNA double helix is approximately 3.4 angstroms (Å).

Length of DNA Fragment = Number of Base Pairs * Length of Each Base Pair

Length of DNA Fragment = 46 * 3.4 Å = 156.4 Å

Therefore, the length of the DNA fragment containing 135 hydrogen bonds and 23 guanine bases is approximately 156.4 angstroms (Å).

Answer:
The correct option is a. 19.04 Å.

Same ans I too got