This set of Physical Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Atomic Units”.
1. How many electrons are present in an atom of the element Potassium?
a) 20
b) 19
c) 18
d) 17
View Answer
Explanation: Since, the atomic number of potassium is 19 which means,
Atomic number of potassium = number of protons = 19
Also, the number of protons is always equal to the number of electrons in an element. Therefore, potassium has 19 electrons.
2. What is the symbol for the element Osmium?
a) O
b) O3
c) Os
d) O2
View Answer
Explanation: Os is the symbol of the element Osmium with an atomic number of 76. It has a bluish-white appearance. It is present in the platinum group. Its traces are found in the alloys of platinum ores. It is a transition metal.
3. What two numbers are always the same in a neutral atom?
a) Protons and Electrons
b) Neutrons and Electrons
c) Neutrons and Protons
d) Mass and protons
View Answer
Explanation: Neutral atoms of each element contain an equal number of protons and electrons. The number of protons determines the atomic number of an element but whereas in ions the electrons may be less or more than the protons.
4. Which subatomic particle number never changes in an element?
a) Electrons
b) Neutrons
c) Protons
d) Mass number
View Answer
Explanation: The number of protons in an element never changes because they are fully stable form of matter so they never decay into anything else. Neutrons and electrons decay under some conditions. Number of protons is the deciding factor in determining the atomic number of an element.
5. Which of the following statements are true about anions and cations?
Statement 1: In anions, the electrons are more than the protons.
Statement 2: In cations, the electrons are less than the protons.
a) Statement 1 is true but statement 2 is false
c) Statement 2 is true but statement 1 is false
c) Statement 1 and statement 2, both are true
d) Statement 1 and statement 2, both are false
View Answer
Explanation: A cation is a positively charged ion, with fewer electrons than protons. An anion is a negatively charged ion, with more electrons than the protons. Because of their opposite charges, both tend to attract each other and readily form ionic compounds.
6. Which of the following subatomic particle is found outside the nucleus?
a) Neutrons
b) Protons and Neutrons
c) Protons
d) Electrons
View Answer
Explanation: Electrons are located outside the nucleus in the electron cloud. Electrons carry negative charges and are much smaller than the nucleus of the atom. They exist in the atoms as spherical shells of various radii, representing different energy levels.
7. Which of the following subatomic particles are found inside the nucleus?
a) Protons
b) Protons and Neutrons
c) Neutrons
d) Electrons
View Answer
Explanation: Protons and neutrons are located inside the nucleus at the center of the atom, electrons are found outside the nucleus. Because opposite charges attract each other, positive nucleus are attracted to the negative electrons.
8. What is the other name for the Wave-Mechanical/Cloud Model?
a) Quantum-Mechanical model
b) Nuclear model
c) Plum Pudding model
d) Planetary model
View Answer
Explanation: Erwin Schrodinger proposed the quantum mechanical method which is also known by the name of Wave-Mechanical/Cloud Model. This model is based on quantum theory, which says matter also has properties associated with waves.
9. What is used when energy in an electron is absorbed?
a) Black-line spectrum
b) Dark-line spectrum
c) Bright-line spectrum
d) Cathode ray tube
View Answer
Explanation: Dark-line spectrum is a spectrum which comes to know when energy absorbs in an electron. This energy absorption results in a transition from a lower energy state to a higher energy state. This produces absorption spectrum which has dark lines.
10. How many electrons are there in Na (sodium)?
a) 6
b) 11
c) 3
d) 22
View Answer
Explanation: Since, the atomic number of Na (sodium) is 11 which means,
Atomic number of Na (sodium) = number of protons = 11
Also, the number of protons is always equal to the number of electrons in an element. Therefore, Na (sodium) has 11 electrons.
11. What kind of charge does the nucleus carry?
a) Positive (+)
b) Negative (-)
c) Neutral
d) Charge of electron
View Answer
Explanation: Nucleus is that dense central core of the atom, contains both protons and neutrons. Because protons have a positive charge and neutrons have no charge thus, nucleus always carry positive charge.
12. Which of the following subatomic particle has the highest mass?
a) Electrons
b) Anion
c) Protons
d) Neutrons
View Answer
Explanation: Neutron has the highest mass because it is the heaviest among all subatomic particles with mass of 1.0087 amu. Proton has a mass of 1.0073 amu which is slightly lower than the neutron and the mass of electron is 0.00055 amu.
13. Where are valence electrons found?
a) Outermost shell/orbital
b) Any orbital
c) Innermost shell/orbital
d) Nucleus
View Answer
Explanation: The number of electrons in the outermost shell of a particular atom determines its reactivity, or tendency to form chemical bonds with other atoms. This outermost shell is known as the valence shell, and the electrons found in it are called valence electrons.
14. What is the general unit when labeling the mass of an atom?
a) Inches
b) Atomic mass units
c) Grams
d) Centimeters
View Answer
Explanation: The universal mass unit, abbreviated u or amu, is defined as one-twelfth of the mass of the carbon-12 atom. The absolute mass of a carbon-12 atom is obtained by dividing the value 12 by the Avogadro number (NA = 6.022×1023).
15. How many neutrons are there in the element Silver (Ag)?
a) 12
b) 47
c) 61
d) 72
View Answer
Explanation: The atomic number and mass number of silver is 47 and 107.86 u respectively.
Atomic number of silver = number of protons = 47
Mass Number of silver = number of protons + number of neutrons = 107.86 u
Therefore, number of neutrons in silver = mass number – number of protons = 107.86 – 47 = 60.86 u (approximately 61).
Sanfoundry Global Education & Learning Series – Physical Chemistry.
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