1. Which subatomic particle did J.J. Thomson identify, and what is its charge?

J.J. Thomson identified electron, which is negatively charged.

2. What was the major challenge before scientists at the end of the 19th century?

Challenge was to reveal the structure of the atom & explain its important properties.

3. How did the study of static electricity lead to the discovery that the atom is not indivisible?

Static electricity study led to the indication that an atom is not indivisible by studying the condition under which electricity is conducted by different substances.

4. What is the conclusion drawn from the activity of rubbing a comb and a glass rod?

The conclusion drawn is that the atom consists of charged particles.

5. What did E. Goldstein discover in 1886, and what is the charge and mass of the particles he discovered?

E. Goldstein discovered positively charged particles (protons) in canal rays. Charge of the proton is +1, the mass is 2000 times the electron.

6. What is the mass and charge of an electron and a positively charged particle, and how are they represented?

Mass of electron is negligible, charge is -1 (represented as e-). Mass of positively charged particle is one unit, the charge assigned is +1 (represented as p+).

7. What is Thomson's model of an atom, and how does he represent the atom?

Thomson proposed atom as a positively charged sphere with electrons embedded in it, similar to a Christmas pudding or a watermelon. Negative and positive charges are equal, so atom as a whole is electrically neutral.

9. What is the major drawback of Rutherford's theory?

The major drawback is that any charged particle moving in a circular path would lose energy and fall into the nucleus, leading to the destruction of the atom, which does not happen.

10. What is Bohr's model of an atom?

Bohr's model explains that only certain discrete orbits of electrons are allowed inside the atom, known as energy levels or shells. Electrons do not radiate energy while revolving in discrete orbits.

11. Who discovered neutrons, and what is their mass and charge?

In 1932, J. Chadwick discovered neutrons in the atom, which have no charge and a mass equal to that of a proton.