Chemistry (Part-I) (UPSC)

Total Questions: 34

11. Most of the explosions in mines occur due to the mixing of : [2000]

(a) hydrogen with oxygen
(b) oxygen with acetylene
(c) methane with air
(d) carbon dioxide with ethane

Correct Answer: (c) methane with air

Solution:Mixing of methane with air is the cause of most mining explosions.

12. In an atom, the order of filling up of the orbitals is governed by : [2001]

(a) Aufbau's principle
(b) Heisenberg's uncertainty principle
(c) Hund's rule
(d) Pauli's exclusion principle

Correct Answer: (a) Aufbau's principle

Solution:Aufbau principle states that 'in the ground state of the atom, the orbitals are filled in order of their increasing energies starting with the orbital of lowest energy. The word aufbau is German word which means building up.

The increasing order of energy and hence that of filling of orbitals is as follows: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p.

13. A radioactive substance has a half-life of four months. Three-fourth of the substance would decay in : [2001]

(a) 3 months
(b) 4 months
(c) 8 months
(d) 12 months

Correct Answer: (c) 8 months

Solution:As it is given that half life of given substance is 4 months.

The amount of substance left after 4 months = 1/2

The amount of substance left after 8 months = 1/4

Therefore the amount of substance decay in 8 months = (1 1/4 )=3/4

14. Which one of the following is NOT radioactive? [2001]

(a) Astatine
(b) Francium
(c) Tritium
(d) Zirconium

Correct Answer: (d) Zirconium

Solution:) Zirconium is not a radioactive element. It is highly ductile and extremely resistant to corrosion and heat. Its symbol in the periodic table is Zr, and its atomic number is 40. It melts at 1855 degrees Celsius (°C) and boils at 4409 deg * C and it is not corroded by acids, alkalis or seawater. The rest three Astatine, Francium and Tritium are radioactive in nature.

15. Match List I with List II and select the correct answer using the codes given below the lists: [2001]

List-I (Characteristic)	List-II (Particle)
A. Zero mass	1. Positron
B. Fractional charge	2. Neutrino
C. Fractional spin	3. Quark
D. Integral spin	4. Photon

Codes:

	A	B	C	D
(a)	2	3	1	4
(b)	3	2	4	1
(c)	2	3	4	1
(d)	3	2	1	4

Correct Answer: (a)

Solution:The Standard Model of particle physics assumed that neutrino are massless.

A quark is an elementary particle and a fundamental constituent of matter. Quarks have fractional electric charge values either - 1/3 or 2/3 times the elementary charge. The positron or antielectron is the antiparticle or the antimatter counterpart of the electron.

The positron has an electric charge of+le, a spin of 1/2 and the same mass as an electron. In physics, a photon is an elementary particle. Spin of a photon can be 1 or +1. In a classical view we can say that one is spinning right and other to the left.

Recently, Scientists have measured neutrino mass with record-breaking accuracy. Scientists have constrained the mass of neutrinos to less than I eV for the first time, breaking an important barrier in neutrino physics.

16. With reference to ionic compounds, consider the following statements: [2003]

1. Ionic compounds are insoluble in alcohol.

2. lonic compounds in the solid state are good conductor of electricity.

Which of these statements is/are correct?

(a) Only 1
(b) Only 2
(c) Both 1 and 2
(d) Neither 1 nor 2

Correct Answer: (a) Only 1

Solution:lonic compound is a chemical compound in which ions are held together in a lattice structure by ionic bonds. Following the aphorism, "like dissolves like", ionic compounds dissolve in polar solvents, especially those that ionize, such as water and ionic liquids. They are usually appreciably soluble in other polar solvents such as alcohols, acetone. Solid ionic compounds cannot conduct electricity because there are no mobile ions or electrons present in the lattice.

17. Regarding the atom of a chemical element, the magnetic quantum number refers to : [2003]

(a) orientation
(b) shape
(c) size
(d) spin

Correct Answer: (a) orientation

Solution:Quantum numbers describe the unique properties and characteristics of electrons within atoms. The magnetic quantum number (m) determines the orbital orientation in space. It specifies the number of orbitals within a subshell and ranges from -1 to +1, including zero. Each value of' l corresponds to a different orientation of the orbital.

18. Which one of the following statements is correct? [2007]

(a) Liquid sodium is employed as a coolant in nuclear reactors.
(b) Calcium carbonate is an ingredient of tooth paste.
(c) Bordeaux mixture consists of sodium sulphate and lime.
(d) Zinc amalgams are used as a dental filling.

Correct Answer: (a) Liquid sodium is employed as a coolant in nuclear reactors.

Solution:Liquid sodium is used as a coolant in nuclear reactors. Sodium is a well-known low-melting-point (97.7°C) alkali metal, which has the main advantages of high thermal conductivity and low neutron absorption cross-section. Also, the relatively high boiling point (882.8°C) of sodium allows a reactor to operate at pressures close to ~0.1 MPa. In addition, very high heat-transfer coefficients can be achieved with sodium cooling. However, sodium is very reactive substance, which requires special precautions, when used as a reactor coolant. On contact with air, it burns; plunged into water, it explodes. Thus, statement (a) is correct.

Toothpaste generally contains the following components:

(a) Water (20-40%)

(b) Abrasives (50%) including aluminum hydroxide, calcium hydrogen phosphates, calcium carbonate, magnesium carbonate, silica, and hydroxyapatite.

Thus, statement (b) is also correct.

Bordeaux mixture is a mixture of copper (II) sulphate (CuSO) and quicklime (CaO) used as a fungicide. Thus, statement (c) is incorrect.
Teeth can be filled with gold; porcelain; silver amalgam (which consists of mercury mixed with silver, tin, zinc, and copper); or tooth-colored, plastic, and materials called composite resin fillings. Thus, statement (d) is incorrect.

19. Which one of the following types of glass can cut off ultraviolet rays? [2007]

(a) Soda glass
(b) Pyrex glass
(c) Jena glass
(d) Crookes glass

Correct Answer: (d) Crookes glass

Solution:Crookes Glass, which incorporates Cerium Oxide (CeO2), effectively blocks ultraviolet (UV) rays due to its high UV absorption properties. This specialized glass is commonly used in the lenses of eyeglasses, particularly sunglasses.

20. In a dry cell (battery), which of the following are used as electrolytes? [2009]

(a) Ammonium chloride and Zinc chloride
(b) Sodium chloride and Calcium chloride
(c) Magnesium chloride and Zinc chloride
(d) Ammonium chloride and Calcium chloride

Correct Answer: (a) Ammonium chloride and Zinc chloride

Solution:A dry cell has the electrolyte immobilized as a paste, with only enough moisture in the paste to allow current to flow. The electrolyte is ammonium chloride in the form of a paste next to the zinc anode.

In some more modern types of so called "high power batteries, the ammonium chloride has been replaced by zinc chloride.

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