Defence GK Questions 2026

In methane the carbon atom is joined to four hydrogen atoms by four single bonds and has no lone pair, so the four bonding pairs push one another as far apart as possible and point to the corners of a regular tetrahedron, with bond angles of about 109.5 degrees.

Rusting is a slow oxidation in which iron combines with oxygen in the presence of moisture to form hydrated iron oxide, the reddish-brown flaky substance we call rust.

Zinc is above hydrogen in the reactivity series, so it displaces hydrogen from a dilute acid: zinc and dilute hydrochloric acid give zinc chloride and hydrogen gas.

A nitrogen atom has five valence electrons and needs three more to complete its octet, so two nitrogen atoms share three pairs of electrons and form a triple bond, written N to N with three lines.

In an ionic or electrovalent bond a metal atom loses one or more electrons to a non-metal atom; the metal becomes a positive ion and the non-metal a negative ion, and the electrostatic attraction between the two holds the compound together, as in sodium chloride and magnesium oxide.

Vegetable oils contain unsaturated fatty acids with carbon-carbon double bonds, and when hydrogen is passed through the oil at about 60 degrees Celsius in the presence of finely divided nickel, the double bonds add hydrogen and become saturated, turning the liquid oil into semi-solid vanaspati.

An amphoteric oxide reacts with both acids and bases to give a salt and water. Aluminium oxide dissolves in hydrochloric acid to give aluminium chloride and in sodium hydroxide to give sodium aluminate, so it behaves as a base in one case and as an acid in the other.

Benzene has the formula C6H6 and a ring of six carbon atoms, each carrying one hydrogen. Count the sigma bonds first: six carbon-carbon bonds around the ring and six carbon-hydrogen bonds give twelve sigma bonds.

Ethylene, also called ethene, has the formula C2H4, and its two carbon atoms share two pairs of electrons, which is a carbon-carbon double bond made of one sigma and one pi bond; it is the simplest alkene.

In a double displacement reaction two compounds exchange their ions, so both reactants must be compounds. Here hydrogen and oxygen are elements combining to form a single product, water, which makes it a combination reaction and also a combustion and redox reaction, but certainly not a double displacement.

A small quantity of fluoride in drinking water protects teeth against decay, but when the concentration rises above the permissible limit it causes fluorosis.

Water hyacinth is an aquatic weed introduced into India from South America.

The mission, working under the Ministry of Jal Shakti, is the implementing agency of the Namami Gange Programme launched in 2014, and it works through State Ganga Committees and district committees along the river.

The Ganga Action Plan was launched in 1985 to intercept, divert and treat the sewage of the towns along the river, and it was the first programme of its kind in India.

The Water (Prevention and Control of Pollution) Act of 1974 was India’s first comprehensive law on pollution.

When fertilisers, detergents and sewage add nitrates and phosphates to a lake or a slow-moving river, algae multiply into a bloom that covers the surface.

Nitrate from fertiliser run-off and from sewage seeps into groundwater; in an infant it is converted to nitrite, which binds to haemoglobin and forms methaemoglobin, a compound that cannot carry oxygen.

Biochemical oxygen demand measures the oxygen that micro-organisms need in order to break down the organic matter present in a sample.

Minamata disease takes its name from Minamata Bay in Japan, where a factory discharged mercury compounds that were converted by bacteria into methylmercury, concentrated in fish through biomagnification and then eaten by people.

Itai-Itai disease was first identified in Japan among people who ate rice grown with water polluted by cadmium from mining waste.