Answer :
1. Answer : (d) n, α, p, e
Explanation: Neutron has no charge, hence e/ m is zero for neutron. Next, a-particle (He2+ ) has very high mass compared to proton and electron, therefore very small e/m ratio. Proton and electron have same charge (magnitude).
2. Answer : (d) 3s, 3p and 3d orbitals all have the same energy
Explanation: In a hydrogen atom, 3s,3p and 3d orbitals will have same energy as all orbitals belonging to the same shell have same energy in hydrogen atom.
3. Answer : (c) Orientation of orbitals
Explanation: Magnetic Quantum Number (ml) specifies the orientation in space of an orbital of a given energy (n) and shape (l). This number divides the subshell into individual orbitals which hold the electrons; there are 2l+1 orbitals in each subshell.
4. Answer : (c) [Kr]4d105s1
Explanation: The electronic configuration of Ag in ground state is [Kr]4d105s1
5. Answer : (a) K
Explanation: K = 19 = 1s22s22p63s23p64s1
3s23p6 = m-shell
= k has only 8 electrons in M shell
6. Answer : (b) Chromium
Explanation: Electrons in M shell (or 3rd shell) = 13
∴ Configuration of M shell : 3s23p63d5
Therefore, the element can be either Cr(Z = 24) or Mn (Z = 25). As Mn is not one of the options given, Cr is the correct answer.
7. Answer : (c)
Explanation: Two electrons in same orbital have opposite spins as; +1/2 & -1/2. Therefore they can be distinguished from their spin quantum number.
8. Answer : (a) 3.4 eV
Explanation: The kinetic energy is equal to the negative of the total energy. The first excited state energy of orbital = -3.4 eV and The kinetic energy of same orbital = -(-3.4 eV) = 3.4 eV.
9. Answer : (d)
Explanation: (i) The electrons in an atom revolve around the nucleus only in certain selected circular paths, called orbits.
(ii) The energy is emitted or absorbed only when the electrons jump from one energy level to another.
10. Answer : (c) 10 electrons
Explanation: n = 6, l = 2 means 6d → will have 5 orbitals.
∴ max 10 electrons can be accommodate as each orbital can have maximum of 2 electrons.
11. Answer : (a) They are electromagnetic waves
Explanation: Cathode rays are not electromagnetic wave because they do not have electric and magnetic components perpendicular to each other.
12. Answer : (a) Air is a poor conductor of electricity under normal conditions
Explanation: Air is a mixture of neutral or inert gases. Therefore it contains few or no charged particles or free ions for conduction of electricity. Hence, air is a poor conductor of electricity.
13. Answer : (a) A beam of neutrons
Explanation: As the neutron is a chargeless particle, hence, the beam of neutrons is not deflected by electrical or magnetic field.
14. Answer : (a) Chadwick
Explanation: In May 1932 James Chadwick announced that the core also contained a new uncharged particle, which he called the neutron.
15. Answer : (a) Overall neutrality of atom
Explanation: Only overall neutrality of an atom could be explained correctly by Thomson model of atom.
16. Answer : (a) neutrons + protons
Explanation: The nucleon number is equal to the total number of nucleons (protons and neutrons) in the nucleus of an atom.
17. Answer : (b) 2
Explanation: Nickel has two unpaired electrons in the 3d sublevel. When nickel ionizes to the +2 state it loses the two electrons in the 4s, so there are still two unpaired electrons in Ni2+
18. Answer : (d) \(\gamma-\)rays
Explanation: Gamma rays are not emitted by the electronic structure of atoms. They are photons, like light, thus they are neutral. Gamma rays are high energy (high frequency) electromagnetic radiation.
19. Answer : (d) 25
Explanation: Number of orbitals in a shell = n2 = (5)2 = 25
20. Answer : (b) 40
Explanation: Atomic weight =70
Atomic number =30
So the Number of neutrons
= At. wt. − At. no.
= 70− 30
= 40
Hence, the total number of neutrons in dipositive zinc ions with the mass number 70 is 40.
21. Answer : (d) 2
Explanation: \(E_1=h.\frac{c}{\lambda_1}\)
\(E_2=h.\frac{c}{\lambda_2}\)
\(\frac{E_1}{E_2}=\frac{hc}{\lambda_1}\times\frac{\lambda_2}{\lambda_1}\)
= 4000/2000
= 2
22. Answer : (a) 22
Explanation: In a neutral atom, atomic number represents the number of protons inside the nucleus and equal number of electrons around it. Therefore, the number of total electrons in molecule of CO2
= electrons present in one carbon atom + 2 x electrons present in one oxygen atom = 6 + 2 x 8 = 22.
23. Answer : (a) CN-
Explanation: Isoelectronic species are the having same number of electrons.
Number of electrons in CO = 6 + 8 = 14
O2- = 16 + 1 = 17
N2+ = 14 - 1 = 13
O2+ = 1 6 - 1 = 15
CN- = 6 + 7 + 1 = 14
Hence, CO isoelectronic with CN− ion.
24. Answer : (b) Hund's rule
Explanation: The explanation for the presence of three unpaired electrons in the nitrogen atom can be given by Hund's rule. According to this rule, electron pairing in any orbital (s, p, d or f) cannot take place until each orbital of the same sublevel contains 1 electron. The electronic configuration of N is 1s22s22p3.2p orbital has 3 sub-levels each of which will contain one electron.
25. Answer : (a) Nucleus
Explanation: Rutherford`s scattering experiment is related to the size of the nucleus of an atom. The objective of experiment demonstrates the scattering of alpha particles by gold foil.
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