Identify the element that helps to trap light energy that is essential for photosynthesis.

The correct answer is C, Hepatitis B. The hepatitis B vaccine was the first vaccine made by recombinant DNA technology. Scientists cut out the gene for the surface protein of the hepatitis B virus and put it into yeast cells; the yeast then made that protein in large amounts, and the purified protein is injected as the vaccine. Because only one viral protein is used and no whole virus is involved, the vaccine cannot cause the disease, which is what makes recombinant vaccines safe. It was licensed in the mid 1980s and in India it is part of the pentavalent shot given to infants. A is wrong because the polio vaccine is either the killed virus of Salk or the weakened live virus of Sabin. B is wrong because no vaccine against AIDS has been licensed so far. D is wrong because the smallpox vaccine used the live vaccinia virus, and the disease was declared eradicated in 1980. Exam tip: hepatitis B, first recombinant vaccine, made in yeast from the surface antigen gene.

The correct answer is C, Planimeter. A planimeter measures the area of any flat shape, however irregular its outline. The user simply traces the boundary of the shape on the map with the instrument's pointer, and a wheel and dial record the area swept, which is then multiplied by the square of the map scale. On a contour map this is how the area enclosed by a contour line, a catchment or a reservoir spread is worked out, so it is a standard tool in survey and irrigation work. A is wrong because areameter is not the accepted name of any such instrument. B is wrong because a clinometer measures the slope of ground or the angle of elevation of a point, not an area. D is wrong because a graphometer is an old surveying instrument used to measure horizontal and vertical angles. Exam tip: planimeter for area, clinometer for slope, planimeter plus contour map for catchment area.

The correct answer is C, 18% Tungsten. High-speed steel is named 18-4-1 after the three metals added to it in that order: 18 per cent tungsten, 4 per cent chromium and 1 per cent vanadium, with iron making up the rest along with a little carbon. Tungsten is the heart of the alloy because it keeps the steel hard even when the cutting edge glows red hot, so drills, milling cutters and lathe tools made from it can cut at high speed without losing their edge. Chromium adds hardness and resistance to rust, and vanadium refines the grain and improves wear resistance. A is wrong because chromium in this grade is 4 per cent, not 1. B is wrong because the 18-4-1 grade has no nickel; nickel goes into stainless steel and into invar. D is wrong because vanadium is the 1 per cent part of the name. Exam tip: 18-4-1 means tungsten 18, chromium 4, vanadium 1.

The correct answer is B, adrenaline. Adrenaline, also called epinephrine, is made by the medulla of the adrenal gland and is the body's emergency hormone; it makes the heart beat faster and stronger and narrows the small blood vessels, so blood pressure rises within seconds. That is why an injection of adrenaline is the first treatment when pressure crashes in shock or in a severe allergic reaction. The same hormone widens the air passages, raises blood sugar and gets the body ready for the fight or flight response. A is wrong because insulin, from the beta cells of the pancreas, lowers blood sugar and is used in diabetes. C is wrong because thyroxine from the thyroid controls the rate of metabolism and growth, and acts slowly over days. D is wrong because vasopressin, the antidiuretic hormone of the pituitary, chiefly saves water by making the kidney reabsorb it. Exam tip: adrenal medulla makes adrenaline, the fight or flight hormone that raises heart rate and blood pressure.

The correct answer is A, Ashwagandha. Ashwagandha, whose botanical name is Withania somnifera, is called winter cherry in English because of the small red berry it bears inside a papery cover; it is also called Indian ginseng. The part used is the root, which in Ayurveda is given as a tonic for weakness, stress and sleeplessness, and the plant's Sanskrit name comes from the horse-like smell of the fresh root. It is a hardy shrub of dry regions, so Rajasthan, Madhya Pradesh and Gujarat are the main growing states; the Nagauri type from Nagaur in Rajasthan and the crop around Mandsaur and Neemuch in Madhya Pradesh are the best known. B is wrong because rose is an ornamental and perfume crop, not a winter cherry. C is wrong because lily is a garden flower grown from bulbs. D is wrong because chandni is an ornamental flowering shrub grown for its white flowers. Exam tip: Ashwagandha, Withania somnifera, winter cherry or Indian ginseng, root used.