Question

Given below are two statements :
one is labelled as
Assertion (A) and the other is labelled as
Reason (R).
Assertion (A) :
UV spectrophotometry is commonly used to estimate nucleic acids.
Reason (R) :
Nucleic acids absorb UV light maximally at 280 nm.
In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

Remember: \[ 260 \text{ nm} \rightarrow \text{Nucleic acids} \] \[ 280 \text{ nm} \rightarrow \text{Proteins} \] Purity of DNA is commonly checked using: \[ \frac{A_{260}}{A_{280}} \] A ratio of about \(1.8\) indicates relatively pure DNA.

Answer 1

The Correct Option is C

Concept: UV spectrophotometry is widely used for quantification of nucleic acids because nucleic acid bases absorb ultraviolet light strongly. The maximum absorbance of nucleic acids occurs at: \[ 260 \text{ nm} \] Proteins, especially aromatic amino acids such as tryptophan and tyrosine, absorb maximally near: \[ 280 \text{ nm} \]

Step 1: Evaluating Assertion (A). The assertion states: \[ \text{UV spectrophotometry is commonly used to estimate nucleic acids} \] This statement is correct because nucleic acid concentration can be measured using absorbance at: \[ A_{260} \] Therefore: \[ \boxed{(A) \text{ is correct}} \]

Step 2: Evaluating Reason (R). The reason states: \[ \text{Nucleic acids absorb UV light maximally at 280 nm} \] This statement is incorrect because: \[ \boxed{\text{Nucleic acids absorb maximally at } 260 \text{ nm}} \] while: \[ 280 \text{ nm} \rightarrow \text{Maximum absorbance for proteins} \] Hence: \[ \boxed{(R) \text{ is incorrect}} \]

Step 3: Selecting the correct option. Since: \[ (A) \text{ is true and } (R) \text{ is false} \] the correct answer is: \[ \boxed{(C)\ (A)\text{ is correct but }(R)\text{ is not correct}} \]