CDS Previous Year GK Questions

Potassium and barium exchange their partner ions: K₂SO₄ and BaCl₂ swap ions to give KCl and BaSO₄. In a double displacement reaction two compounds exchange ions.

Statements 1 and 2 are correct; statement 3 is wrong because zinc is more reactive than iron.

Too little fluoride weakens tooth enamel and makes teeth prone to decay, known as dental caries. Fluoride becomes part of the enamel as fluorapatite, which resists the acids made by mouth bacteria from sugars.

Quartz is crystalline silicon dioxide (SiO₂), an electrical insulator, not a semiconductor. A semiconductor has a conductivity between that of a conductor and an insulator, and its conductivity rises with temperature or when impurities are added (doping).

With equal length and area, the wire of lower conductivity, aluminium, has the higher resistance. Resistance is R = ρl/A, where ρ is resistivity, and resistivity is the reciprocal of conductivity (ρ = 1/σ).

A candle gives light by burning wax, so it converts chemical energy, not electrical energy, into light and heat. In a burning candle the wax vapour combines with oxygen in the air; the chemical energy stored in the wax is released as heat and light.

Dr. B. R. Ambedkar founded the All India Scheduled Castes Federation at Nagpur in July 1942. The Federation was formed as a political party to fight for the rights of the Scheduled Castes as a separate group.

Make in India was launched in 2014, not 2018, and fostering innovation is one of its stated objectives. Prime Minister Narendra Modi launched Make in India on 25 September 2014 to turn India into a global hub for design and manufacturing.

The black layer on old silver is silver sulphide (Ag₂S). Air contains traces of sulphur compounds, mainly hydrogen sulphide (H₂S) from burning fuels and decaying matter.

Bauxite, a hydrated aluminium oxide (Al₂O₃·2H₂O), is the main ore from which aluminium is extracted. Bauxite is first purified into alumina (aluminium oxide) by the Bayer process.

A guard tube is filled with anhydrous calcium chloride, which absorbs moisture and keeps the hydrogen chloride gas dry. In the school experiment, hydrogen chloride gas is made by heating sodium chloride with concentrated sulphuric acid, and the gas is passed through a guard tube containing calcium chloride.

The gastric glands in the stomach wall secrete hydrochloric acid, the only mineral (inorganic) acid among the options. Hydrochloric acid (HCl) makes the stomach strongly acidic, with a pH of about 1.5 to 3.5.

Pitch is the way our ear senses the frequency of a sound: the higher the frequency, the higher the pitch.

Institutional training, overseas employment and leveraging of public infrastructure are all sub-missions of the National Skill Development Mission.

When houses are built all around a lake or tank, the village grows in a ring around the water, giving a circular pattern.

The Office of the United Nations High Commissioner for Refugees won the Nobel Peace Prize in 1954 and again in 1981.

A rainbow forms only because sunlight is refracted, dispersed and internally reflected inside raindrops. When sunlight enters a water droplet it is refracted and split into its colours (dispersion), because each colour bends by a different amount.

Both a plane mirror and a convex mirror always form an erect, virtual image, whatever the distance of the object.

Iron is a transition (d-block) element, and such elements can show more than one oxidation state. In transition metals the energies of the outer s electrons and the inner d electrons are very close, so atoms can lose different numbers of electrons.

Helium is a noble gas whose atoms exist singly, so it is a monatomic gas, not a diatomic one. Helium has a completely filled first shell (1s²), so its atoms have no tendency to share electrons or bond with each other.