Important Questions (1 mark): Structure of the Atom - Class 9 MCQ

Electron is presents in all atoms. So, electron is regarded as universal particle.Electron are distributed in shell around the nucleus.

The main subatomic particles of nucleus are proton and neutron. Electrons are located in different shells of an atom.

Number of protons in the nucleus of an atom is equal to atomic number. Sum of number of proton and neutron present in nucleus is called mass number.

An isotopes of Hydrogen called protium does not contain any neutron. It contain one electron and one proton.

Anode rays were discovered by E. Goldstein as canal rays. They are positively charged particles.

Mass number of an atoms is equal to the sum of number of proton and neutron present in the nucleus of the atom. So, mass number of given element = 14 +13 = 27 u.

In his model of atom, Rutherford stated that electrons present in the extra nuclear portions are not stationary rather they revolve around the nucleus at high speed following circular path.

Atomic mass of Nitrogen is 14 u and number of protons in nucleus is 7. So, number of neutron = Mass number – number of protons = 14-7 = 7.

In an alpha scattering,few alpha particles rebounded because both alpha particle and nucleus have positive .So,the both of these particles repel each other and nucleus is very dense so alpha particles rebounded.

Atomic number is defined as the number of protons present in the nucleus of an atom.

The radius of extra nuclear portion is more than that of the nucleus of an atom. Nuclear region is small portion of atom as compared to whole atom by 10⁵ times.

The correct answer is D as its atomic number is 2

it contains 2 electrons and in order to from He2+ ion, it will have to lose its 2 electrons.

Neil Bohr got the noble prize for the work on the structure of atom. He proposed the Bohr model of atom having desecrate shell in which electrons are distributed

The correct answer is B as the α-particle scattering experiment gave totally unexpected results.
The following observations were made: 
(i) Most of the fast moving -particles passed straight through the gold foil. 
(ii) Some of the -particles were deflected by the foil by small angles.
(iii) Surprisingly one out of every 12000 particles appeared to rebound.

Magnesium (Mg) contains 12 proton and mass number is 24. Number of neutron is equal to mass number – number of proton present in nucleus. So, number of neutron = 24-12 = 12.

Anion contain more electron than proton because anion are formed by receiving electrons from other atoms.

The order of shell around the nucleus is in order of K, L, M, N from nucleus to outward. So, L shell is nearer to the nucleus than M shell.

The nucleus is made up of protons and, in most cases, neutrons. An atomic nucleus is much, much smaller than an atom. The cloud of electrons that "orbit" the nucleus and define the "size" of an atom is roughly 100,000 times as large as that atom's nucleus. Atoms can be stable or unstable depending on the balance of forces within their nucleus and the state of their outer shell: