The scientist who discovered the mutagenic nature of $X$-rays and ultraviolet $(UV)$ radiation is......

What is the effect of a change in a single base pair of $DNA$?

Assertion $(A)$: Mutation results in changes in genotype and phenotype of an organism.
Reason $(R)$: Mutation leads to alteration of $\text{DNA}$ sequences,i.e.,variations in $\text{DNA}$.
Choose the correct answer from the options given below.

Who introduced 'artificial transmutation' by $X$-rays?

Normally $DNA$ molecule has $A-T$ and $G-C$ pairing. However,these bases can exist in alternative valency status,owing to rearrangements called:

Write a short note on Mutation.