RRB Group D 2022 Previous Year GK Questions with Answers

The correct answer is A, un-deviated. A ray that passes through the optical centre of a thin lens comes out in the same direction, without any bending. The optical centre is the central point of the lens on its principal axis. Near it the two faces of the lens are almost parallel, like a thin glass slab, so the ray shifts sideways by a negligible amount and keeps its direction. This is one of the three standard rays used to draw ray diagrams: a ray parallel to the principal axis passes through the focus after refraction in a convex lens, a ray through the focus comes out parallel to the axis, and a ray through the optical centre goes straight on. B is wrong because only rays that strike the lens away from the centre are deviated. C is wrong because bent means the same as deviated, which does not happen at the centre. D is wrong because a lens refracts light; reflection is what mirrors do. Exam tip: through the optical centre = straight through; parallel ray = through the focus; ray through the focus = emerges parallel.

The correct answer is D, (i) - (c), (ii) - (b), (iii) - (a). Red cabbage is a natural acid-base indicator, methyl orange is a synthetic acid-base indicator, and onion and clove are olfactory indicators. An indicator tells whether a solution is acidic or basic. Natural indicators come from plants: litmus from lichen, turmeric, red cabbage leaves and coloured petals such as hydrangea and petunia. Synthetic indicators made in the laboratory include methyl orange, which is red in acid and yellow in base, and phenolphthalein, which is colourless in acid and pink in base. Olfactory indicators change their smell instead of their colour; onion, vanilla and clove lose their smell in a basic solution. A is wrong because it calls methyl orange an olfactory indicator. B is wrong because it labels red cabbage as olfactory. C is wrong because it puts onion and clove under natural colour indicators. Exam tip: change of smell = olfactory (onion, clove, vanilla); change of colour = litmus, turmeric, red cabbage; lab-made = methyl orange, phenolphthalein.

The correct answer is D, Hg. Mercury (Hg) belongs to group 12, not group 11. Group 11 of the modern periodic table holds copper (Cu, atomic number 29), silver (Ag, 47) and gold (Au, 79). These three are called the coinage metals because coins were made from them; each has one electron in its outermost s orbital, which makes them soft and shiny, and silver and copper are the best conductors of electricity of all metals. Mercury sits right next to gold in period 6 but in group 12, together with zinc and cadmium, and it is the only metal that is liquid at room temperature. A is wrong because silver is a group 11 metal. B is wrong because gold is also in group 11. C is wrong because copper heads group 11. Exam tip: Group 11 = Cu, Ag, Au (coinage metals); Group 12 = Zn, Cd, Hg; the liquid metal mercury is never a coinage metal.

The correct answer is A, Platelets. Platelets are the tiny cell fragments that rush to a cut and start the clot. They are also called thrombocytes and are made in the bone marrow from large cells called megakaryocytes. A healthy adult has about 1.5 to 4 lakh platelets per cubic millimetre of blood, and each one lives for only 8 to 10 days. At a wound they stick together to form a plug and release chemicals that turn the soluble protein fibrinogen into fibrin threads, which trap blood cells and seal the leak. B is wrong because plasma proteins such as fibrinogen take part in clotting, but the paper marks platelets as the component that starts and aids clot formation. C is wrong because white blood cells fight infection, not bleeding. D is wrong because red blood cells carry oxygen with haemoglobin. Exam tip: RBC = oxygen, WBC = immunity, platelets = clotting; a falling platelet count is what dengue is known for.