RRB Group D GK Questions 2026

Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.

Pitchblende, or uraninite, is the chief ore of uranium, the fuel used in most nuclear power stations. Pitchblende is a heavy, black mineral made mostly of uranium oxide.

Portland cement is made by heating a mix of limestone, which supplies lime, with clay, which supplies silica and alumina.

Traditional solder is an alloy of lead and tin, often in a ratio of about 60 parts tin to 40 parts lead.

The trapped steam raises the pressure inside the cooker, and at higher pressure water boils at a higher temperature, so food cooks faster.

Mercury(II) oxide is a red-orange solid, mercury is a liquid metal at room temperature, and oxygen is a gas. This is a thermal decomposition reaction: when mercuric oxide is heated, it breaks down into mercury and oxygen, written with states as 2HgO(s) → 2Hg(l) + O₂(g).

One mole of N₂ weighs 28 g, so half a mole weighs 14 g. A nitrogen molecule is made of two nitrogen atoms, each with an atomic mass of 14 u, so its molecular mass is 28 u and its molar mass is 28 g per mole.

Planck's constant has the dimensions [ML²T⁻¹], exactly those of angular momentum. From E = hf, h = E / f. Energy has dimensions [ML²T⁻²] and frequency has [T⁻¹], so h has [ML²T⁻²] ÷ [T⁻¹] = [ML²T⁻¹], with the SI unit joule-second.

Soft sand gives way slowly, so the person is brought to rest over a longer time and the force on the body is smaller.

A Mach number greater than 1 means the body is moving faster than sound in the surrounding medium. The Mach number is the ratio of a body's speed to the speed of sound in the medium around it, named after the Austrian physicist Ernst Mach.

An object denser than the liquid sinks, and one less dense than the liquid floats. By Archimedes' principle, a body placed in a liquid feels an upward buoyant force equal to the weight of the liquid it displaces.

Milk is a colloid in which tiny droplets of fat are dispersed in water, so it is not uniform at the microscopic level and counts as a heterogeneous mixture.

The apple's gravitational potential energy first becomes kinetic energy as it falls, some is lost as heat to the air on the way, and at impact the rest goes into heating the ground and apple and into sound.

Diamond and graphite are allotropes of the same element, carbon, so their chemical properties are the same; only their physical properties differ.

In the electrolytic refining of copper, a solution of copper sulphate made acidic with a little dilute sulphuric acid carries the copper ions between the electrodes.

Two ammonium ions, each with a charge of +1, are needed to balance one carbonate ion with a charge of -2.

Putting a soft iron bar inside a solenoid makes the magnetic field much stronger, so the claim that the field stays the same is not correct.

Magnesium combines with oxygen to form a new substance, magnesium oxide, so a chemical reaction takes place. When a magnesium ribbon is heated, it burns with a dazzling white flame and leaves a white powder: 2Mg + O₂ → 2MgO.

The nitride ion, N³⁻, carries a charge of minus three, so its valency is -3. Nitrogen has five electrons in its outer shell.

A telescope's objective must gather as much light as possible from a distant object and form a large image, so it is both wide and of long focal length.