Reason
In $$\alpha-$$ decay the mass number decreases by $$4$$ and atomic number decreases by $$2$$ In $$\beta-$$ decay the mass number remains unchanged, but atomic number increases by $$1$$ only.
Assertion
$$z^{X^{A}}$$ undergoes $$2\alpha-$$ decays. $$2\beta-$$ decays and $$2\gamma-$$ decays and the daughter product is $$z-2^{Y^{A-8}}$$
$$z^{X^{A}}$$ undergoes $$2\alpha-$$ decays. $$2\beta-$$ decays and $$2\gamma-$$ decays and the daughter product is $$z-2^{Y^{A-8}}$$
A
Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
B
Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
C
Assertion is correct but Reason is incorrect
D
Both Assertion and Reason are incorrect
Correct option is A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
After the first two $$\alpha$$ decays the mass number will decrease by $$8$$ and the atomic number will decrease by $$4$$ which will make,
$$_{z-4}X^{A-8}$$
After the next two $$\beta$$ decays, the atomic number will increase by 2 units. The product will be,
$$_{z-2}X^{A-8}$$
After the last two $$\gamma$$ decays, the atomic number and the mass number will remain unchanged. Final daughter product is
$$_{z-2}X^{A-8}$$
The assertion is therefore correct and the reason is also correct which is the correct explanation for assertion.
The answer is option (A).