The discovery of subatomic particles helped in understanding the atomic structure. Class 9

The discovery of subatomic particles helped in understanding the atomic structure. Class 9

Question 1.

Assertion (A): The discovery of subatomic particles helped in understanding the atomic structure. Class 9

Reason (R): The number of electrons is equal to the number of protons in an atom.

Choose the correct statement:

(i) Both A and R are true, but R is not the correct explanation of A.

(ii) Both A and R are true, and R is the correct explanation of A.

(iii) A is true, but R is false.

(iv) A is false, but R is true.

Answer:

(ii) Both A and R are true, and R is the correct explanation of A.

Explanation:

The Assertion (A) is true. The discovery of subatomic particles (electrons by Thomson, protons and nucleus by Rutherford, neutrons by Chadwick) was crucial in helping scientists understand the structure of the atom. Each discovery led to a better and more accurate model of the atom.

The Reason (R) is also true. In a neutral atom, the number of electrons is always equal to the number of protons. This is a fundamental fact that ensures atoms are electrically neutral.

However, R is not the correct explanation of A. The equal number of electrons and protons is a consequence (result) of atomic neutrality - it tells us something about the balance of charge in an atom. It does not explain how or why the discovery of subatomic particles helped understand atomic structure. The discovery of subatomic particles helped understand atomic structure by revealing what atoms are made of, how their mass is distributed, and how they are arranged - not merely because electrons equal protons.