Chemistry (Part-2) (CDS-Solved Paper)

Red phosphorus is a relatively stable allotrope of phosphorus at room temperature. Its ignition temperature (543 K) is much higher than that of white phosphorus (303 K). As a result, it does not catch fire easily.

Law of definite proportion by volume was propounded by Joseph Louis Gay Lussac and is applicable for gases.
● Law of multiple proportion was propounded by John Dalton in 1803.
● Law of definite proportion by weight was propounded by Joseph Proust.
● Law of conservation of mass was propounded by Antoine Lavoisier.

The density of ice is less than that of water and thats why, ice floats on water. The ice structure takes up more volume than the liquid water molecules, hence ice is less dense than liquid water. Hence, statements (d) is not correct.

Diamond is used as an abrasive for sharpening hard tools. Graphite is used as a dry lubricant in machines running at high temperature, where oil cannot be used as a lubricant.

The atomic theory of matter was first proposed by an English chemist, John Dalton. The theory said that all matter is made of atoms. Atoms are indivisible and indestructible. All atoms of a given element are identical in mass and properties. Compounds are formed by a combination of two or more different kinds of atoms.

Natural resources such as coal, petroleum and natural gas take thousands of years to form naturally and cannot be replaced as fast as they are being consumed. That is why, it is a non-renewable resource. While natural resources such as solar energy, water and fisheries are renewable resources.

Acetylene is a fuel used in gas welding. It is used to weld and cut the metals that have a temperature of 3300°C of a flame.

The correct matching is A→ 2, B → 1, C → 3, D → 4.
● Chlorofluorocarbon (DFCs) is responsible for depletion in ozone layer.
● Acid rain is caused by a chemical reaction that begins, when compounds like sulphur dioxide and nitrogen oxide are released into the air.
● Lead compound is harmful for human nervous system.
● The primary greenhouse gases in earth’s atmosphere are water vapour, carbon dioxide, methane and nitrous oxide.

Lithium metal is used in mobile phone batteries. Nickel-cadmium batteries are used in the portable electronics and toys whereas, zinc-carbon batteries are used in the electrical appliances. These are non-rechargeable batteries.

Burning of plastic wastes and burning of dry and fallen leaves in a garden field both creates air pollution. Use of chemical fertilisers in agricultural field creates soil pollution and other harmful effect on environment. Treatment of domestic sewage before its release is the best practice in respect of healthy environment.