This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “D and F-Block Elements – Actinoids”.
1. Actinoid compounds are more basic than lanthanoid compounds.
Explanation: Lanthanoids are involved in the filling of 4f- orbitals, whereas actinoids are involved in the filling of 5f-orbitals. The binding energy of 4f electrons is comparatively less than that of 5f-electrons. The compounds formed by lanthanides are less basic, whereas the compounds of actinides are highly basic.
2. Which property of actinoids cannot be explained?
Explanation: Their magnetic properties cannot be explained easily, as they are more complex. The 5f bands formed due to 5f-5f wave function overlap or to hybridisation with s, p or d electrons. As a result of the band formation, a wide variety of magnetic phenomena may occur.
3. Which is the most stable oxidation state of actinoids?
Explanation: Actinoids show variable oxidation states because of the smaller energy gap between 5f, 6d and 7s orbitals. Though 3+ is the most stable oxidation state, other oxidation states are possible because of the good shielding of f-electrons.
4. All actinoids are diamagnetic in nature.
Explanation: Substances which are weakly repelled by a magnetic field are said to be diamagnetic. All actinoids are paramagnetic in nature due to the presence of unpaired electrons. This means that they are weakly attracted by a magnetic field.
5. Actinoids are mostly attacked by which acid?
a) Hydrochloric acid
b) Nitric acid
c) Sulphuric acid
d) Boric acid
Explanation: Actinoids are highly reactive metals especially in the finely divided state. All these metals are attacked by hydrochloric acid but the effect of nitric acid is very small due to the formation of a protective oxide layer on their surface.
6. Which of the actinoids is used in the treatment of cancer?
Explanation: Thorium (atomic no.90, symbol-Th) is used in atomic reactors and in the treatment of cancer. Its salts are used in making incandescent gas mantles. Thorium is formed by the radioactive of uranium and is used to treat tumours.
7. Which of the actinoids is used as a nuclear fuel?
Explanation: Uranium is used as fuel in nuclear reactors. It is mined and goes through refining and enrichment before being loaded into a nuclear reactor. Nuclear power plants use a certain kind of uranium, referred to as U-235, for fuel because its atoms are easily split apart.
8. Which isotope of plutonium is used in nuclear bombs?
Explanation: The most common plutonium isotope formed in a typical nuclear reactor is the fissile Pu-239, formed by neutron capture from U-238 (followed by beta decay), and which when fissioned yields much the same energy as the fission of U-235.
9. Choose the correct statement.
a) Both actinoids and lanthanoids are less basic
b) Both actinoids and lanthanoids do not show same oxidation of +3
c) Both actinoids and lanthanoids do not exhibit magnetic and spectral properties
d) Both actinoids and lanthanoids are electropositive
Explanation: Lanthanides and actinides involve filling of f-orbitals and thus are similar in many respects. The most common oxidation state is +3 for both lanthanides and actinides. Both are electropositive in nature and thus very reactive. Magnetic and spectral properties are exhibited by both lanthanides and actinides.
10. Which was the first transuraniumactinoid element to be discovered?
Explanation: Neptunium was the first transuranium element to be discovered in 1940. It is a silvery metal, with a melting point of 637°C and a boiling point of 4174°C. It exhibits oxidation states of +3 to +7 in compounds and useful for chemical experiments.
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