General Science GK Questions with Answers – Page 56

Silver turns black in air because it reacts with sulphur compounds, mainly hydrogen sulphide, to form a thin black coating of silver sulphide (Ag₂S).

In the alkane series the boiling point rises as the carbon chain gets longer, and this order goes from 3 to 4 to 5 to 8 carbons.

An electron's mass is about 1/1836 of a proton's, which is roughly 1/2000. The electron has a mass of about 9.1 × 10⁻³¹ kg, while the proton has about 1.67 × 10⁻²⁷ kg, nearly 1,836 times heavier.

SONAR uses sound waves under water to find the distance and direction of objects. A SONAR set on a ship has a transmitter that sends out pulses of ultrasound and a detector that picks up their echo from the sea bed, a shoal of fish, a wreck or a submarine.

The sulphide ion has 16 + 2 = 18 electrons, and its mass number of 32 is its count of nucleons.

Rutherford's gold foil experiment showed that an atom's positive charge and almost all its mass sit in a tiny central nucleus.

Tendons are made of tightly packed parallel bundles of collagen fibres, which give them great pulling strength. Collagen is the most abundant protein in the human body.

AIDS is caused by HIV, a retrovirus whose genome is two copies of single-stranded RNA. After HIV enters a helper T-cell (CD4 cell), its enzyme reverse transcriptase copies the viral RNA into DNA, which is then built into the host cell's own DNA.

With no work done, the first law of thermodynamics reduces to ΔU = Q, so the change in internal energy equals the heat that flows in or out.

Its network of membrane tubes and sheets forms channels that carry materials, especially proteins, between parts of the cytoplasm and the nucleus.

Growth with repair and metabolism are two of the features that mark living beings off from non-living things. A living body grows from inside by making new cells from the food it takes in, and it heals wounds and replaces worn-out tissue.

A nerve impulse is carried by the movement of sodium ions into the nerve cell and potassium ions out of it.

Lemon juice is acidic and rich in vitamin C, which together slow the enzyme reaction that browns cut apple. When an apple is cut, the enzyme polyphenol oxidase in its cells meets oxygen in the air and oxidises the fruit's phenolic compounds into brown pigments (melanins).

In a micelle it is the long hydrocarbon tail that points into the oil droplet, while the ionic end faces outward into the water, so statement D reverses the real picture.

Light from the bottom bends as it passes from water into air, so the bottom seems nearer than it really is.

The heat given out by 2 g of steam equals the heat taken in by 250 g of water, and that balance gives L = 550 Cal/g. The water warms from 20°C to 25°C, so it absorbs 250 × 1 × 5 = 1250 Cal.

When oxygen runs short during hard exercise, muscle cells break glucose down anaerobically, and lactic acid is the by-product. In glycolysis, which takes place in the cytoplasm, one molecule of glucose splits into two molecules of pyruvate and yields a little ATP.

Both statements are true, and the magnetic field set up by the current (Statement II) is exactly why the compass needle turns (Statement I).

The pancreas pours amylase, trypsin and lipase into the duodenum in its juice, so all three classes of food are digested there.

Lymph is plasma that has leaked out of the capillaries, and red blood cells are too large to pass through the capillary walls.