Structure of Atom - Online Test

Q1. According to quantum mechanics ψ2(r) the wave function squared gives
Answer : Option D
Explaination / Solution:

Probability density of finding an electron at a point with in an atom, it is posible to predict region around the nucleus where electron can most probably be found. ψ has no physical significance while ψ2 represnts the probability density of finding an electron.

Q2. Due to the presence of electrons in the inner shells, the electron in the outer shell will not experience the full positive charge of the nucleus (Ze). This is known as
Answer : Option A
Explaination / Solution:

Shielding effect can be defined as a reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces of the electrons on the nucleus. It is also referred to as the screening effect (or) atomic shielding.

Q3. The Aufbau principle states : In the ground state of the atoms, the orbitals are filled in order of
Answer : Option D
Explaination / Solution:

The Aufbau Principle states that in the ground state of an atom, an electron enters the orbital with lowest energy first and subsequent electrons are fed in the order of increasing energies. The word 'aufbau' in German means 'building up'. Here, it refers to the filling up of orbitals with electrons.

Q4. According to Pauli’s exclusion principle
Answer : Option A
Explaination / Solution:

The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers. As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.

Q5. Daltons atomic theory could not explain one of the following
Answer : Option C
Explaination / Solution:

Daltons theory said atom is indivisible in nature so it doesnot explain the existence of subatomic particles. The indivisibility of an atom was proved wrong: an atom can be further subdivided into protons, neutrons and electrons. However an atom is the smallest particle that takes part in chemical reactions.

Q6. Oil drop experiment is for determining the
Answer : Option B
Explaination / Solution:

The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron). The experiment entailed observing tiny electrically charged droplets of oil located between two parallel metal surfaces, forming the plates of a capacitor.

Q7. How many neutrons and protons are there in the   nucleus?
Answer : Option A
Explaination / Solution:

Number of protons = Atomic number =6 Number of neutrons = atomic mass - no of protons = 13-6 = 7

Q8. Cathode rays are discharged under one of the following conditions:
Answer : Option C
Explaination / Solution:

Production of cathode rays Cathode rays are produced in the discharge tube by applying the following conditions:

  • A high potential difference (>1200 V) is applied across the two aluminium electrodes.
  • The length of the tube is 30 cm and the diameter is 3 cm.
  • Pressure inside the tube is maintained below 0.01 mm of Hg.

Q9. One of the following scientists was the first to discover electron
Answer : Option B
Explaination / Solution:

Electron was discovered by J. J. Thomson in 1897 when he was studying the properties of cathode ray. J. J. Thomson won Nobel Prize in 1906 for discovering the elementary particle electron.

Q10. Experiments on electrical discharge through gases ultimately lead to the discovery of
Answer : Option B
Explaination / Solution:

Towards the end of the 19th century Joseph J.Thomson (1856-1940) was studying electric discharges at the well-known Cavendish laboratory in Cambridge, England. Several people had been studying the intriguing effects in electric discharge tubes before him. Spectacular glows could be observed when a high voltage was applied in a gas volume at low pressure. It was known that the discharge and the glow in the gas were due to something coming from the cathode, the negative pole of the applied high voltage. Thomson made a series of experiments to study the properties of the rays coming from the cathode. He observed that the cathode rays were deflected by both electric and magnetic fields - they were obviously electrically charged. By carefully measuring how the cathode rays were deflected by electric and magnetic fields, Thomson was able to determine the ratio between the electric charge (e) and the mass (m) of the rays. Thomson's result was 

The particle that J.J.Thomson discovered in 1897, the electron, is a constituent of all the matter we are surrounded by. All atoms are made of a nucleus and electrons. He received the Nobel Prize in 1906 for the discovery of the electron, the first elementary particle.