General Science GK Questions with Answers – Page 123

All three are genetic disorders, caused by changes in genes or chromosomes and passed on through birth, not by germs.

Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air.

Potential difference is the work done to move a unit charge between two points, and its SI unit is the volt.

An iron, toaster, oven, kettle and heater all turn electrical energy into heat when current flows through a coil of high resistance.

A concave lens spreads the light rays slightly before they enter the eye, so the image moves back onto the retina.

Adrenaline is made by the adrenal glands, which sit like caps on top of the two kidneys. It is released in fear, anger or sudden danger, so it is called the "fight or flight" hormone.

The nucleus is called the master or control centre of the cell because it directs all the activities of the cell.

Brass is an alloy of copper and zinc, usually about 70 per cent copper and 30 per cent zinc. Adding zinc makes brass harder than pure copper, gives it a golden-yellow shine and helps it resist corrosion.

Bleaching powder gives off chlorine when it reacts with water, and this chlorine does the bleaching and kills germs. Bleaching powder is calcium oxychloride, CaOCl2, made by passing chlorine gas over dry slaked lime, Ca(OH)2.

Carbon dioxide reacts with lime water to form calcium carbonate, which does not dissolve, and its fine white particles make the water look milky.

Vitamin K is needed to make the clotting proteins, so without it even a small cut keeps bleeding. The liver uses vitamin K to make prothrombin and other clotting factors that turn blood into a clot at a wound.

The medulla oblongata is the breathing centre of the brain, which is why we keep breathing even while asleep. It is the lowest part of the hindbrain and joins the brain to the spinal cord.

Washing soda is sodium carbonate decahydrate: each unit of sodium carbonate holds ten molecules of water of crystallisation. It is made from common salt in steps: baking soda is heated to get anhydrous sodium carbonate, called soda ash, which is then recrystallised from water to give washing soda crystals.

Red has the longest wavelength in visible light, about 700 nm, so the tiny particles of air, fog, smoke and dust scatter it the least.

The reactivity series lists metals from the most reactive to the least reactive, and potassium heads it because it loses its single outer electron most easily.

It gives the direction of the force, and so of the motion, on a current-carrying conductor placed in a magnetic field, which is exactly what turns the coil of a motor.

Combustion means burning in oxygen, and complete burning of methane gives carbon dioxide, water, heat and light. The equation is balanced: one carbon, four hydrogen and four oxygen atoms on each side.

The N shell is the fourth shell (n = 4), and the most electrons a shell can hold is given by the formula 2n², so 2 × 4² = 32.

In diamond every carbon atom is joined to four other carbon atoms by strong covalent bonds. These bonds point towards the corners of a tetrahedron and build a rigid three-dimensional network that runs through the whole crystal.

It is the standard set of rules used for reflection by spherical mirrors and for the mirror formula. Under this convention the pole of the mirror is the origin and the principal axis is the x-axis.