Atomic Structure -

1. Two elements X and Y have the following electronic configurations:
X: 1s² 2s²2p⁶ 3s² 3p¹
Y: 1s² 2s² 2p⁴
Which compound are these elements most likely to form?

A. X₂Y
B. X₃Y₂
C. X₂Y₃
D. XY₃

Answer

Correct Option: C.
Option A Explained
One X atoms loses three electrons, so two X atoms six electrons. One Y accepts two eelctrons, so the number of electrons lost by two X atoms is not equal to the number of electrons gained by one Y atom. This means that the formula X₂Y is wrong.
Option B Explained
Thsi formula is wrong because three X atoms lose nine electrons while two Y atoms accepts four electrons. The electrons lost are not equal to the electrons gained.
Option C Explained
This is correct formula because two X atoms loses six electrons while three Y atoms accepts six electrons. The number of electrons lost are equal to the number of electrons gained so the ration 2:3 is correct.
Option D Explained
One X loses three electrons while three Y require six electrons, so the number of electrons lost and gained are not equal.

2. How does the energy difference between successive energy levels in a hydrogen atom change as the principal quantum number increases?

A. It increases.
B. It decreases
C. It first increases and then decreases.
D. It first decreases and then increases.

Answer

Correct Option: B.
Option A Explained
Higher energy levels become closer together, not farther apart.
Option B Explained
The spacing between energy levels decreases as the electron moves farther from the nucleus.
Option C Explained
There is only one trend, that is the energy difference bteween successive shells decreases.
Option D Explained
There is always decrease in energy gap between the shells as we move away from the nucleus.

3. Which of the following particles determine the chemical behavior of an atom by participating directly in ordinary chemical reactions?

A. protons only
B. neutrons only
C. electrons only
D. electrons and sometimes protons

Answer

Correct Option: C.
Option A Explained
Protons remain inside the nucleus and do not participate in chemical reactions.
Option B Explained
Neutrons also remain inside the nucleus and nerver participate in chemical reactions.
Option C Explained
Chemical reactions involve the gain, loss, or sharing of electrons. In ionic bonds, electrons are transferred while in covalent bonds they are shared.
Option D Explained
Only electrons participate in ordinary chemical reactions. Protons and neutrons never take part in chemical reactions, rather they take part in nuclear reactions.

4. Which of the following electromagnetic radiations has the longest wavelength?

A. Infrared rays
B. Ultraviolet rays
C. Gamma rays
D. X-rays

Answer

Correct Option: A.
Option A Explained
Infrared rays have longer wavelengths than ultraviolet, X-rays, and gamma rays.
Option B Explained
Ultraviolet rays have shorter wavelengths than visible light.
Option C Explained
Gamma rays have the shortest wavelengths
Option D Explained
X-rays have shorter wavelengths than ultraviolet and infrared radiation.

5. A continuous absorption spectrum is produced mainly by:

A. Excited atoms
B. Excited molecules
C. Ground state molecules
D. Ground-state atoms

Answer

Correct Option: C.
Option A Explained
Excited atoms usually produce emission line spectra.
Option B Explained
Excited molecules produce continueous emission spectra because they continuously emit energy absorbed by them already.
Option C Explained
Ground-state molecules absorb energy and give continuous absorption spectra. Molecules give continuous spectra.
Option D Explained
Ground-state atoms generally produce line absorption spectra. Atoms give line spectra due to electron transition between shells.

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