Sindh Mdcat Exclusive Course Chemistry Atomic Structure — Solved MCQs

Question 1

The presence of several fine lines in a line spectrum shows the presence of:

Accepted Answer

C. Sub shells — A. Shells (Incorrect): Fine lines in a line spectrum are indicative of transitions between energy levels within an atom, not the presence of shells, which represent broad electron distribution regions. B. Energy levels (Incorrect): Fine lines in a line spectrum indeed indicate the presence of energy levels within an atom. However, it does not directly show the presence of sub-shells, which are further divisions within energy levels. C. (correct) It is because of sub energy levels.Previously the energy of sub energy level was considered to be equal but it actually differs by about 10−4 ev. Hence fine spectral lines are produced.D. This option is not correct.

Question 2

Which of the following does not show variable valency?

Accepted Answer

C. Zn — The electronic configuration of zinc is [Ar]3d10 4s2 It can only lose two electrons from the 4s orbital and show +2 oxidation state. It does not show variable valency. However, all other transition metals like Mn, Fe, Co have partially filled d orbitals and hence, show variable valency.

Question 3

Name the orbital n = 5; l = 2; m = 0.

Accepted Answer

B. 5d — Quantum numbers are the basis of the sequence, arrangement, shape, and orientation of the elements in periodic table. N = 5 indicates the 5th energy level (5th period of the periodic table or the 5th principal quantum number) L = 2 indicates the shape of the orbital (2 corresponds d-orbital-shaped quantum number) M = 0 indicates the orientation of the orbital (z - axis magnetic quantum number)

Question 4

Which of the following shows the Planck's quantum theory?

Accepted Answer

C. E = hv — In chemistry, Frequency is denoted by vSo, the Planck's quantum theory isE = hv where h is the Planck's constantIt can be rewritten asE = hc/λ since frequency(v) = c/λ where c is the speed and λ is the wavelength.

Question 5

The mass of proton is _ times heavier than _.

Accepted Answer

D. 1836, electrons — Remember that the mass of a proton is 1836 times heavier than that of an electron.

Question 6

The shielding effect of inner electrons is responsible for:

Accepted Answer

A. Decreasing ionization energy — The shielding effect of inner electrons causes a decrease in attraction between the nucleus and the outer electrons of the atom. Hence, it is easier to remove the outer electrons, which decreases the ionization potential. Therefore, options B and C are incorrect Option D is incorrect because 'Electronegativity' is a measure of an atom's ability to attract shared electrons to itself, and due to the decrease in attraction between the nucleus and the outer electrons, electronegativity will also decrease.

Question 7

Maximum number of electrons in a subshell is given by:

Accepted Answer

B. 2 (2l + 1) — l = azimuthal quantum numberl values: s=0 , p=1, d=2, f=3Number of orbitals in a subshell: 2l+1You can check this for the 1st shell: 2(0) +1= 1Number of electrons in a shell = 2 x number of orbitals (as each orbital has a maximum of 2 electrons)Therefore,2(2l+1)

Question 8

Orbitals having the same energy are called:

Accepted Answer

B. Degenerate orbitals — Degenerate orbitals are the orbitals of the same subshell having equal energies. When the electrons of the orbitals are not influenced by any external factors like an electric field or magnetic field, they have the same energies.

Question 9

Quantum number values for 2p orbitals are:

Accepted Answer

A. n=2,l = 1 — There are two types of quantum numbers: azimuthal quantum number(l) and principal quantum number(n). The principal quantum number,n, is actually the number of shells. Azimuthal quantum number, l, is actually the number of subshells. According to n-1 rule for the azimuthal quantum number, l will be equal to 1. “2p”, where 2 represents the “n=2” and p represents the second subshell hence “l=1”.

Question 10

Which of the following is the electronic configuration of Potassium(K) Atomic number= 19K?

Accepted Answer

D. 1s2, 2s2, 2p6, 3s2, 3p6, 4s1 — Option D is the correct option because this is the only option that has 19 electrons by adding manually.

Question 11

Which of the following statements is correct?

Accepted Answer

D. Chadwick experiment shows the presence of neutrons — Option D is correct. Chadwick bombarded a sample of beryllium with alpha particles and observed a new form of radiation that was not affected by electric fields. He concluded that this radiation consisted of neutral particles, which he named neutrons. Neutrons have no electric charge but have a mass similar to protons.

Question 12

"In an atom no two electrons can have the same set of four Quantum numbers" is stated by:

Accepted Answer

C. Pauli's Exclusion principle — The set of numbers used to describe the position and energy of the electron in an atom are called quantum numbers. There are four quantum numbers namely, principal, azimuthal, magnetic and spin quantum numbers. Pauli's exclusion principle states that in an atom no two electrons can have the same set of four quantum numbers. Let us take example of electrons in Helium, both have all quantum numbers same except spin quantum number, one is clockwise and other is anti-clockwise.

Question 13

The radii of the second orbit of the hydrogen atom calculated from Bohr's model is:

Accepted Answer

C. 2.116 Å — R = 0.529 0.529 x n2/z 0.529 x 4Å 2.116 Å

Question 14

The neutron was discovered by:

Accepted Answer

D. Chadwick — Thomson discovered electrons in 1897, Chadwick discovered neutrons in 1932 and Goldstein discovered canal ray in 1886.

Question 15

The ground state of an atom corresponds to a state of :

Accepted Answer

B. Minimum energy — The nucleus of an atom is surrounded by electrons that occupy shells or orbitals of varying energy levels. The ground state of an electron, the energy level it normally occupies, is the state of lowest energy for that electron.

Question 16

Shape of the orbital occupied by an electron is defined by:

Accepted Answer

B. Azimuthal quantum number — The shape of the orbital can be s,p,d, or f. This shape is determined by the azimuthal quantum number. The spin quantum number tells us about the type of spin electron possessed in an orbital. The principal quantum number tells us about the no.of the shell, not the shape of the orbital.

Question 17

The Balmer series lies in which region of the electromagnetic spectrum?

Accepted Answer

B. Visible — The Balmer series lies in the visible region of the electromagnetic spectrum.

Question 18

If uncertainty in the position of an electron is zero, the uncertainty in it's momentum is?

Accepted Answer

E. Infinite — According to Heisenberg's uncertainty principle, it is impossible to measure position x and momentum p simultaneously. Use ∆x∆p ≥ h/4π as ∆x → 0, ∆p → ∞ Here, neither uncertainty can be zero and if the position is zero the uncertainty in momentum becomes infinite.

Question 19

Choose the value of the Rydberg constant among the following values:

Accepted Answer

A. 1.09678 x 107 m-1 — You’ll have to rote learn this. Memorise the power and units.

Question 20

Diamond is a bad conductor because it:

Accepted Answer

C. Has no free electron in the crystal — A good conductor has a large presence of free electrons, as they are not bonded strongly to the nucleus, and allow conduction of charges to take place.

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