How much work is done in moving a charge of 2 coulomb across two points having a potential difference of 5V?

The correct answer is B, tuberculosis (TB). The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis. In India it is given as a single dose soon after birth under the Universal Immunisation Programme, and it protects infants mainly from the severe forms of the disease, such as tuberculous meningitis and miliary tuberculosis. Tuberculosis itself is caused by the bacterium Mycobacterium tuberculosis, identified by Robert Koch in 1882, and it spreads through droplets when a patient coughs. Option A is wrong because typhoid, caused by Salmonella typhi, has its own conjugate vaccine. Option C is wrong because mumps is a viral disease covered by the MMR vaccine along with measles and rubella. Option D is wrong because plague, caused by Yersinia pestis and carried by rat fleas, needs a different vaccine. Exam tip: BCG at birth for TB, and World TB Day falls on 24 March.

The correct answer is A, Ethanol. CH3CH2OH, also written C2H5OH, is ethanol or ethyl alcohol, the second member of the alcohol family. The -OH group attached to the carbon chain is the functional group that makes it an alcohol. Ethanol is a colourless liquid that boils at about 78 degrees Celsius, mixes with water in every proportion, and is used in alcoholic drinks, as a solvent in medicines and in ethanol-blended petrol. Alcohol free of water is called absolute alcohol, while alcohol made unfit for drinking by adding methanol and a dye is called denatured spirit. Option B is wrong because acetic acid, the acid in vinegar, is CH3COOH and carries the -COOH group. Option C is wrong because chloroform is CHCl3, once used as an anaesthetic. Option D is wrong because methane is CH4, the simplest hydrocarbon and the main part of natural gas. Exam tip: -OH means an alcohol and -COOH means a carboxylic acid.

The correct answer is C, increase in area of contact reduces pressure exerted. Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure. The weight of the bag stays exactly the same whether the strap is thin or wide, but a wide strap spreads that weight over more of the shoulder, so the shoulder feels less pressure and the strap does not cut into the skin. The same idea explains why school bags, seat belts and the wide tyres of a tractor are made broad. A is wrong because it states the relation upside down, since pressure falls when area rises. B and D are wrong because the force is simply the weight of the load and the width of the strap cannot change it; only the pressure changes. Exam tip: P equals F divided by A, so broad straps and flat feet reduce pressure while sharp knives and pointed nails increase it.

The correct answer is D, the statement that atmospheric pressure is negligible. Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all. We do not feel it because the pressure of the blood and other fluids inside the body pushes outward with the same force, and the two balance. A is a correct statement because pressure is force divided by area, so the same force on a smaller area gives more pressure, which is why knives are sharpened and nails are pointed. B is correct because a liquid presses in every direction, on the bottom as well as on the side walls, and the push grows with depth. C is correct because the column of air above us has weight and therefore presses on us. Exam tip: P equals force divided by area; atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal.

The correct answer is B, sulphurous acid. Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3. Sulphur dioxide is an oxide of a non-metal, and such oxides are acidic in nature, which is why the solution turns blue litmus red. The same gas, released when coal and diesel burn, dissolves in rain water in the air and is then slowly oxidised further, so sulphur dioxide is one of the main causes of acid rain. A is wrong because sulphur trioxide is made by oxidising sulphur dioxide with more oxygen over a catalyst, not by dissolving it in water. C is wrong because sulphuric acid is formed when sulphur trioxide, and not sulphur dioxide, meets water. D is wrong because sulphur is the element itself and cannot be got back simply by dissolving its oxide. Exam tip: SO2 with water gives H2SO3; SO3 with water gives H2SO4.