In the NDA & NA (II) 2017 Exam, the question from chemistry covered key areas such as – gases, acides, semi conductors, etc. For the benefit of the NDA aspirants, Jagran Josh is providing chemistry questions, answers along with detailed explanation.
1. Which one of the following gases is placed second in respect of abundance in the Earth's atmosphere?
(d) Carbon dioxide
Ans. (a) Oxygen
The permanent gases whose percentages do not change from day to day are nitrogen, oxygen and argon. Nitrogen accounts for 78% of the atmosphere, oxygen 21% and argon 0.9%. Gases like carbon dioxide, nitrous oxides, methane, and ozone are trace gases that account for about a tenth of one percent of the atmosphere.
2. When pure water boils vigorously, the bubbles that rise to the surface are composed primarily of
(c) hydrogen and oxygen
(d) water vapour
Ans. (a) air
When pure water boils vigorously, the bubbles that rise to the surface are composed primarily of air. The bubbles are mostly nitrogen with oxygen and a bit of argon and carbon dioxide.
3. Which one among the following chemicals is used as washing soda?
(a) Calcium carbonate
(b) Calcium bicarbonate
(c) Sodium carbonate
(d) Sodium bicarbonate
Ans. (c) Sodium Carbonate
Sodium carbonate (Na2CO3), which is also known as washing soda, is the water-soluble sodium salt of carbonic acid. It most commonly occurs as a crystalline decahydrate, which readily effloresces to form a white powder, the monohydrate.
4. Why is potassium permanganate used for purifying drinking water?
(a) It kills germs
(b) It dissolves the impurities
(c) It is a reducing agent
(d) It is an oxidizing agent
Ans. (d) It is an oxidizing agent
Potassium permanganate used for purifying drinking water since it is an oxidizing agent. Similarly, chlorine is a strong oxidant commonly used in water treatment for oxidation and disinfection.
5. Which one of the following is a cause of acid rains?
(c) Sulphur dioxide
(d) Carbon monoxide
Ans. (c) Sulphur dioxide
Acid rain is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acid rains.
6. The desirable range of pH for drinking water is
(a) 6.5 to 8.5
(b) 5.0 to 6.5
(c) 6.5 to 7.0
(d) 7.0 to 8.5
Ans. (a) 6.5 to 8.5
As per the standards set by the Environmental Protection Agency (EPA) of the USA, drinking water must have a pH value of 6.5-8.5.
7. How much CO2 is produced on heating of 1 kg of carbon?
(a) 11/3 kg
(b) 3/11 kg
(c) 4/3 kg
(d) 3/4 kg
Ans. (a) 11/3 kg
It means that 1 kg of carbon requires 8 / 3 kg of oxygen for its complete combustion, and produces 11 / 3 kg of carbon dioxide gas. The value is arrived at by combining the two values.
8. The principal use of hydrofluoric acid is
(a) in etching glass
(b) as a bleaching agent
(c) as an extremely strong oxidizing agent
(d) in the preparation of strong organic fluorine compounds
Glass etching comprises the techniques of creating art on the surface of glass by applying acidic, caustic, or abrasive substances. Because of its high reactivity toward glass, the hydrofluoric acid is used in etching glass.
9. The majority charge carriers in a p-type semiconductor are
(a) free electrons
(b) conduction electrons
Ans. (d) holes
When the trivalent atoms such as Boron or Gallium are added to the intrinsic semiconductor, a p-type semiconductor is formed. In p-type semiconductor, large number of holes is present. Hence, holes are the majority charge carriers in the p-type semiconductor. The holes (majority charge carriers) carry most of the electric charge or electric current in the p-type semiconductor.
10. The ionization energy of hydrogen atom in the ground state is
(a) 13.6 MeV
(b) 13.6 eV
(c) 13.6 Joule
Ans. (c) 13.6 eV
For a hydrogen atom, composed of an orbiting electron bound to a nucleus of one proton, an ionization energy of 2.18 × 10 −18 joule (13.6 electron volts) is required to force the electron from its lowest energy level entirely out of the atom.
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