Solved Practice Questions on Halogen and Noble Gas Family | Inorganic Chemistry PDF Download

Q.1. Helium is the second most abundant gas in the universe.
(a) True
(b) False

Correct Answer is Option (a)
Helium is the second element in the periodic table and has an atomic number of 2. Helium is formed as the result of the fusion of two hydrogen atoms. Helium is the most abundant gas in the universe (23% as compared to 76% of hydrogen). 

Q.2. Group 17 elements are also called halogens.
(a) True
(b) False

Correct Answer is Option (a)
Group 17 elements are called halogens. The name halogen (Greek, halo = sea salts, genes = producing) meaning sea salt formers was given to them by Schweigger in 1811 because the salts (chlorides, bromides and iodides) of the first three elements occur in sea water. 

Q.3. Which of the following noble gases do not occur in the elemental state in the atmosphere?
(a) Helium
(b) Neon
(c) Argon
(d) Radon

Correct Answer is Option (d)
Radon is the last-named member of the 18^th group of elements in the periodic table. It is radioactive in natureand as a result, all other noble gases except radon occur in the elemental state in the atmosphere. 

Q.4. Which of the following element is most reactive?
(a) Chlorine
(b) Fluorine
(c) Bromine
(d) Iodine

Correct Answer is Option (b)
Of all the halogens, fluorine is the most reactive and hence is also called super halogen. Fluorine is also the most electronegative (EN = 4.0) element in the periodic table. This indicates that fluorine has a high tendency to gain electrons from other elements with lower electronegativities. 

Q.5. Which of the following halogen is radioactive?
(a) Fluorine
(b) Bromine
(c) Astatine
(d) Chlorine

Correct Answer is Option (c)
Astatine (Atomic No. = 85, Symbol-At) is radioactive and hence occurs in nature only in traces. Therefore, not much is known about its chemistry, though it might be expected to be a metalloid.

Q.6. Which of the following is the second most abundant noble gas in the atmosphere?
(a) Helium
(b) Argon
(c) Neon
(d) Krypton

Correct Answer is Option (c)
Argon is the most abundant noble gas in the atmosphere, accounting for about 0.934% by volume. Neon is the second most abundant noble gas in the atmosphere (about 0.00182%) followed by helium as the third most abundant noble gas (about 0.000524%). 

Q.7. Halogens do not occur in the free state.
(a) True
(b) False

Correct Answer is Option (a)
Halogens are highly reactive elements and hence do not occur in the free state or native state. They mainly occur in the combined state in the form of their halide (X^–) salts although iodine also occurs as iodate (IO₃^–). 

Q.8. The main commercial source of helium is natural gas.
(a) True
(b) False

Correct Answer is Option (a)
The main commercial source of helium is natural gas which mainly contains hydrocarbons along with varying amounts of carbon dioxide, nitrogen, hydrogen sulphide and helium (2-7%). 

Q.9. Which of the following is not a mineral of fluorine?
(a) Fluorspar
(b) Cryolite
(c) Fluoroapatite
(d) Carnallite

Correct Answer is Option (d)
Fluorine occurs as insoluble fluorides to the extent of 0.07% in the earth’s crust. The chief minerals of fluorine are:

• Fluorspar, CaF₂
• Cryolite, Na₃AlF₆
• Fluoroapatite, CaF₂.3Ca₃(PO₄)₂

Q.10. Which of the following scientists first discovered helium in the solar spectrum during a total solar eclipse?
(a) Lord Rayleigh
(b) J N Lockyer
(c) William Ramsay
(d) Antoine Lavoisier

Correct Answer is Option (b)
J N Lockyer first discovered helium in the solar spectrum during a total solar eclipse on 18^th August, 1868. Later on, in 1895, it was discovered on the planet Earth by a scientist named William Ramsay. 

Q.11. What is the half-life of radon?
(a) 10 days
(b) 4.56 days
(c) 3.82 days
(d) 5.46 days

Correct Answer is Option (c)
Half-life of a radioactive substance refers to the amount of time that it takes for half of the radioactive atoms in a sample to decay into a more stable form. Radon has a half-life of 3.82 days. 

Q.12. What are the decay products of radium?
(a) Radon and oxygen
(b) Radon and nitrogen
(c) Lanthanum and oxygen
(d) Radon and Helium

Correct Answer is Option (d)
Radium is a radioactive element with the atomic number 88. It is the 6^th element in group 2 of the periodic table. Radium (Ra) on radioactive decay, gives Radon (Rn) and Helium (He) as the products. 

Q.13. Which of the following noble gases is not obtained via fractional distillation?
(a) Krypton
(b) Argon
(c) Neon
(d) Helium

Correct Answer is Option (d)
Neon, argon, krypton and xenon are obtained by fractional distillation of air. Fractional distillation of liquid air gives oxygen, nitrogen and a mixture of noble gases. The individual noble gases are then separated by adsorption over coconut charcoal which adsorbs different gases at different temperatures. 

Q.14. Which of the following statements is incorrect about noble gases?
(a) They are monoatomic
(b) They are colourless
(c) They are odourless
(d) They all have an outer electronic configuration of ns²np⁶

Correct Answer is Option (d)
The general outer electronic configuration for noble gases is ns²np⁶. But, for helium, the outer electronic configuration is 1s² as it its atomic number is only 2. All noble gases are monoatomic, odourless and colourless. 

Q.15. What is the ratio of the molar heat at constant pressure to the molar heat at constant volume for a noble gas?
(a) 1.5
(b) 1.67
(c) 1.73
(d) 1.37

Correct Answer is Option (b)
All noble gases are monoatomic in nature due to their stable outer electronic configuration. The ratio of their specific or molar heat at constant pressure to the specific or molar heat at constant volume is equal to 1.67, which is the same for all monoatomic gases.