Q19 of 64 Page 110

Which of the following are true for an element?

(i) Atomic number = number of protons + number of electrons


(ii) Mass number = number of protons + number of neutrons


(iii) Atomic mass = number of protons = number of neutrons


(iv) Atomic number = number of protons = number of electrons

Mass number is always equal to the number of protons plus the number of neutrons and Atomic number is always equal to the number of protons which is equal to the number of electrons to maintain the neutrality of the atom.


Hence, option D is correct.

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17

The nucleus of hydrogen atom is known as:

 18

Which of the following statements about Rutherford’s model of atom are correct?

(i) Considered the nucleus as positively charged.


(ii) Established that the - particles are four times as heavy as a hydrogen atom


(iii) Can be compared to solar system


(iv) Was in agreement with Thomson’s model

 20

Atomic models have been improved over the years. Arrange the following atomic models in the order of their chronological order:

(i) Rutherford’s atomic model


(ii) Thomson’s atomic model


(iii) Bohr’s atomic model

 21

The presence of protons and neutrons at the centre of the atom was suggested by: