1.
The density of dots in a region represents the probability density of finding electrons in the region.The probability density plots of 1s and 2s orbitals are given in Fig. On the basis of below diagram which of the following statements is incorrect?
Correct Answer
D. The probability density of electrons for 2s orbital decreases uniformly as distance from the nucleus increases.
Explanation
The density of dots in the given diagram represents the probability density of finding electrons in a region. The diagram shows that the probability density of electrons for the 2s orbital decreases uniformly as the distance from the nucleus increases. This means that the statement "The probability density of electrons for 2s orbital decreases uniformly as distance from the nucleus increases" is correct, not incorrect. Therefore, the correct answer is that none of the statements are incorrect.
2.
Which of the following statements about the electron is incorrect?
Correct Answer
B. The mass of electron is equal to the mass of neutron.
Explanation
The statement "The mass of electron is equal to the mass of neutron" is incorrect. The mass of an electron is much smaller than the mass of a neutron. The mass of an electron is approximately 1/1836th of the mass of a neutron.
3.
Two atoms are said to be isobars if:
Correct Answer
D. Sum of the number of protons and neutrons is same but the number ofprotons is different.
Explanation
Isobars are atoms that have the same sum of the number of protons and neutrons but a different number of protons. This means that they have the same mass number (since it is the sum of protons and neutrons) but a different atomic number (since it is the number of protons). Therefore, the correct answer is that isobars have the same sum of the number of protons and neutrons but a different number of protons.
4.
Which of the following is responsible to rule out the existence of definite paths or trajectories of electrons?
Correct Answer
B. Heisenberg’s uncertainty principle.
Explanation
Heisenberg's uncertainty principle states that it is impossible to simultaneously determine the exact position and momentum of an electron. This principle introduces a fundamental uncertainty in the behavior of subatomic particles, including electrons, and it implies that there are no definite paths or trajectories for electrons. Therefore, Heisenberg's uncertainty principle is responsible for ruling out the existence of definite paths or trajectories of electrons.
5.
Total number of orbitals associated with third shell will be __________.
Correct Answer
C. 9
Explanation
The third shell corresponds to the n=3 energy level in an atom. According to the quantum mechanical model, each energy level can hold a maximum of 2n^2 electrons. Therefore, the third shell can hold a maximum of 2(3^2) = 18 electrons. Since each orbital can hold a maximum of 2 electrons, the total number of orbitals associated with the third shell will be 9.
6.
Orbital angular momentum depends on __________.
Correct Answer
A. L
Explanation
Orbital angular momentum depends on the quantum number l. The orbital angular momentum of an electron in an atom is determined by its orbital shape, which is characterized by the value of the quantum number l. The larger the value of l, the higher the orbital angular momentum. This means that the shape of the electron's orbital influences its angular momentum, but other quantum numbers such as n, m, and s do not directly affect it.
7.
If travelling at same speeds, which of the following matter waves have the shortest wavelength?
Correct Answer
B. Alpha particle (He ^{2+})
Explanation
Alpha particles (He 2+) have the shortest wavelength among the given matter waves when traveling at the same speeds. This is because the wavelength of a particle is inversely proportional to its mass. Since alpha particles have a larger mass compared to electrons, neutrons, and protons, they will have a shorter wavelength.
8.
Lyman series of spectral lines appear in the ________________ portion of spectrum.
Correct Answer
A. UV
Explanation
The Lyman series of spectral lines appear in the UV portion of the spectrum. This is because the Lyman series corresponds to transitions of electrons in hydrogen atoms from higher energy levels to the n=1 energy level. These transitions result in the emission of photons with higher energy, which corresponds to the UV region of the electromagnetic spectrum.
9.
The correct sequence of sub-shells according to AUFBAU principle follows:
Correct Answer
A. 3s, 3p, 4s, 3d, 4p
Explanation
According to the AUFBAU principle, electrons fill the sub-shells in order of increasing energy. The 3s sub-shell is filled before the 3p sub-shell because it has lower energy. Similarly, the 4s sub-shell is filled before the 3d sub-shell because it has lower energy. Finally, the 4p sub-shell is filled after the 3d sub-shell. Therefore, the correct sequence of sub-shells according to the AUFBAU principle is 3s, 3p, 4s, 3d, 4p.
10.
The frequency of line spectrum is 5.09 × 10^{14} Hz. Its wavelength (in Nano meter) will be: [Given: Speed of light, c = 3 × 10^{8} m/s]
Correct Answer
C. 589 nm
Explanation
The wavelength of a wave can be calculated using the formula: wavelength = speed of light / frequency. In this case, the frequency is given as 5.09 × 10^14 Hz and the speed of light is given as 3 × 10^8 m/s. Plugging these values into the formula, we get wavelength = (3 × 10^8 m/s) / (5.09 × 10^14 Hz). Simplifying this expression gives us the wavelength of approximately 589 nm.
11.
The electronic configuration of atom is [Ne] 3s^{2} 3p^{3 }.The symbol of the element is:
^{ }
Correct Answer
B. P
Explanation
The electronic configuration [Ne] 3s2 3p3 corresponds to the element phosphorus (P).
12.
The wavelengths of two photons are 2000 A^{O} and 4000 A^{O} respectively. What is the ratio of their energies?
Correct Answer
D. 2
Explanation
The energy of a photon is directly proportional to its frequency, which is inversely proportional to its wavelength. Therefore, the ratio of the energies of two photons is equal to the inverse ratio of their wavelengths. In this case, the ratio of the wavelengths is 4000/2000 = 2, so the ratio of their energies is 1/2.
13.
The number of electrons in one molecule of CO_{2} are:
Correct Answer
A. 22
Explanation
The molecule of CO2 consists of one carbon atom and two oxygen atoms. The atomic number of carbon is 6, and the atomic number of oxygen is 8. Therefore, one molecule of CO2 contains 6 + 2(8) = 22 electrons.
14.
Which of the following postulates does not belong to Bohr's model of the atom?
Correct Answer
D. The change in the energy levels of electrons is continuous.
Explanation
Bohr's model of the atom was based on the idea that electrons exist in discrete energy levels or shells. According to this model, electrons can only transition between these energy levels by absorbing or emitting specific amounts of energy. This explains the spectral lines observed in atomic spectra. However, the statement "The change in the energy levels of electrons is continuous" contradicts this postulate. In Bohr's model, the energy levels are quantized, meaning that they can only take on specific values. Therefore, this statement does not belong to Bohr's model of the atom.
15.
The presence of one electron in each of the three 2p sub-shell of nitrogen is explained by:
Correct Answer
B. Hund's rule
Explanation
Hund's rule states that when electrons occupy orbitals of equal energy, they will first fill each orbital with one electron before pairing up. In the case of nitrogen's 2p sub-shell, there are three orbitals with equal energy. According to Hund's rule, each orbital will be singly occupied by one electron before any of them pair up. Therefore, the presence of one electron in each of the three 2p sub-shell of nitrogen is explained by Hund's rule.
16.
To give designation to an orbital (read orbital, not sub-shell), we need:
Correct Answer
D. Principal, Azimuthal and Magnetic quantum number
Explanation
To give designation to an orbital, we need the principal quantum number to determine the energy level or shell in which the orbital is located. The azimuthal quantum number determines the shape of the orbital, indicating whether it is an s, p, d, or f orbital. The magnetic quantum number determines the orientation of the orbital within the subshell. Therefore, all three quantum numbers - principal, azimuthal, and magnetic - are required to fully describe and designate an orbital.
17.
Which of the following statement is not true about the quantum numbers n, l, m_{l}, m_{s}
Correct Answer
A. M_{l} gives information on the energy of the electron in a given orbital
Explanation
The statement that ml gives information on the energy of the electron in a given orbital is not true. The quantum number ml, also known as the magnetic quantum number, determines the orientation or spatial orientation of an orbital within a subshell. It specifies the number of orbitals and their orientation within a given subshell. On the other hand, the principal quantum number n determines the size and energy of the orbital, while the azimuthal quantum number l determines the shape of the orbital. The spin quantum number ms determines the direction of spin of the electron within the orbital.
18.
The Balmer series of spectral lines arise when an electron in an excited Hydrogen atom jumps from an energy level
Correct Answer
D. N = 5 to n = 2
Explanation
The Balmer series of spectral lines arise when an electron in an excited Hydrogen atom jumps from a higher energy level (n = 5) to a lower energy level (n = 2). This transition results in the emission of visible light with specific wavelengths that correspond to the Balmer series. The other options (n = 5 to n = 1, n = 5 to n = 3, n = 5 to n = 4) do not represent transitions within the Balmer series and therefore do not explain the observed spectral lines.
19.
Which of the following set of quantum numbers is not valid?
Correct Answer
A. N = 1, l = 2
Explanation
This set of quantum numbers is not valid because the value of l cannot be greater than or equal to the value of n. In this case, n = 1 and l = 2, which violates this rule. The value of l represents the orbital angular momentum and it can only take values from 0 to (n-1).
20.
Which of the following is not the characteristic of Planck's Quantum theory of radiation?
Correct Answer
A. The energy is not absorbed or emitted in whole number or multiples of quantum
Explanation
Planck's Quantum theory of radiation states that energy is absorbed or emitted in whole number or multiples of quantum, which means that energy is quantized. This is in contrast to classical physics, where energy is considered to be continuous. Therefore, the statement "The energy is not absorbed or emitted in whole number or multiples of quantum" is not a characteristic of Planck's Quantum theory of radiation.
21.
An isotone of _{32}Ge^{76} is:
Correct Answer
C. Only (ii) and (iv)
Explanation
The correct answer is Only (ii) and (iv). This means that an isotone of 32Ge76 can only have the same number of neutrons as 32Ge76, which is 32, and can also have the same number of protons as 32Ge76, which is 32. Therefore, options (i) and (iii) are incorrect as they do not satisfy both conditions. Option (ii) satisfies the condition of having the same number of neutrons, and option (iv) satisfies the condition of having the same number of protons, making them the correct choices.