Point mutation is a change which involves

$A$ mutant microorganism is unable to synthesize a component required for its growth,but it is able to grow if that component is provided. This is called a/an......

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.

Chemical mutagens are considered more dangerous than radiations because:

Hugo de Vries proposed the Mutation theory by studying the plant called . . . . . . .

Mutation is an error that occurs during cell division.