Directions: Choose the correct option:

Assertion $\left(A\right):$ Prototherians are egg laying mammals.

Reason $\left(R\right):$ They act as a connecting link between reptiles and mammals.

1. Both assertion$\left(A\right)$ and reason$\left(R\right)$ are true and reason$\left(R\right)$ is the correct explanation for assertion$\left(A\right).$
2. Assertion$\left(A\right)$ is false and reason$\left(R\right)$ is true.
3. Both assertion$\left(A\right)$ and reason$\left(R\right)$ are true, but reason$\left(R\right)$ is not the correct explanation for assertion.
4. Assertion$\left(A\right)$ is true and reason$\left(R\right)$ is false.

The correct option is A Both assertion$\left(A\right)$ and reason$\left(R\right)$ are true and reason$\left(R\right)$ is the correct explanation for assertion$\left(A\right).$

Correct option: $\left(a\right)$Both assertion$\left(A\right)$ and reason$\left(R\right)$ are true and reason$\left(R\right)$ is the correct explanation for assertion$\left(A\right).$

$\bullet$ Prototheria includes the primitive egg-laying mammals like platypus and echidna.

$\bullet$ In these animals, after the eggs hatch, mothers feed their young ones with their milk.

$\bullet$ Laying eggs is a reptilian character while feeding the young ones with mammary glands is a mammalian character.

$\bullet$ So, the Prototheria acts as a connecting link between reptiles and mammals.

$\bullet$ So the correct answer is $\left(a\right)$.