Question

Assertion: Sodium reacts with oxygen to form $N{{a}_{2}}{{O}_{2}}$ but potassium reacts with oxygen to form $K{{O}_{2}}$
Reason: Potassium is a more reactive metal than sodium.
A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.
C. Assertion is correct but Reason is incorrect.
D. Both Assertion and Reason are incorrect.

Answer 1

Sodium is a chemical element represented by the symbol Na and has atomic number 11 while potassium is also a chemical element having the symbol K and has atomic number 19. Both soft, silvery-white metals which can be cut with the knife.

Complete answer:
Both the metals sodium and potassium have only one valence electron in its outermost shell and due to this reason they both are highly reactive in nature. We know that the size increases as we move down the group due to the increase in the number of shells. Potassium is kept exactly under the sodium which describes sodium is lesser in size as compared to potassium.
Due to the lesser size of sodium it combines with less amount of oxygen and form sodium peroxide represented by $N{{a}_{2}}{{O}_{2}}$ while potassium has bigger size as compare to sodium and it forms superoxide like $K{{O}_{2}}$.
Potassium is a more reactive metal than sodium. But this is not the correct explanation for the potassium to form superoxide and sodium to form peroxide. So we can say that Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion.

Thus option B is the correct answer.

Note:
There are major uses of sodium and potassium metal like sodium chloride is used as common salt, sodium bicarbonate is used as baking agent and sodium hydride is used as a base for various reactions in organic chemistry while potassium element has many biological applications.