General Science GK Questions with Answers – Page 11

Silver reacts with sulphur compounds in the air, mainly hydrogen sulphide, and forms a black coating of silver sulphide. This blackening is the tarnishing of silver, a kind of corrosion.

Osmosis is the passage of water from where water is more concentrated (a dilute solution) to where it is less concentrated, across a membrane that lets water through but holds back solutes.

Ferromagnetism needs the atomic magnets of a substance to line up together in fixed regions called domains, and this happens only in the ordered structure of a solid.

Chemical reactions involve only the outer, or valence, electrons, so these decide how an element behaves. Atoms combine by losing, gaining or sharing their valence electrons to reach a stable arrangement, usually eight electrons in the outer shell.

Animal cells are bounded only by a flexible plasma membrane and have no rigid cell wall outside it. A cell wall is found in plants, where it is made mainly of cellulose, in fungi, where it is made of chitin, and in bacteria, where it is made of peptidoglycan.

Cytokinins are the plant hormones whose main job is to promote cell division, or cytokinesis, which gives them their name.

The blind spot is the place where the optic nerve leaves the eye, and it has no rods or cones, so light falling there is not seen.

The eye lens focuses light on the retina, the light-sensitive layer at the back of the eye, where a real and inverted image is formed.

Starlight is bent again and again as it passes through layers of air whose temperature and density keep changing, so the star seems to flicker in brightness and position.

The packet’s density is 800 g divided by 1,000 cm³, which is 0.8 g/cm³, less than the density of both liquids.

For any position of a real object in front of a convex mirror, the image forms behind the mirror between P and F. A convex mirror bulges outward, and its focus and centre of curvature lie behind it.

The force exerted by light depends on how much light falls on the surface, so with the same intensity, half the area receives half the light and feels half the force.

Particles in a colloid are large enough to scatter a beam of light, which makes the path of the beam visible.

Refractive index is the ratio of the speed of light in air to its speed in the medium, so the speed in glass is c divided by 3/2, which is (2/3)c. The absolute refractive index of a medium is n = c/v, where c is the speed of light in…

In 1913 the English physicist Henry Moseley showed that atomic number, not atomic mass, is the fundamental property of an element.

Pyruvate, the ion of pyruvic acid (CH3COCOOH), is a three-carbon molecule. It is formed at the end of glycolysis, the first stage of respiration, which takes place in the cytoplasm of every living cell.

For a photon, energy equals momentum multiplied by the speed of light, E = pc, so a momentum of 10 MeV/c gives an energy of exactly 10 MeV.

Cotton soaks up sweat well, and as that sweat evaporates from the cloth it takes heat away from the body and keeps us cool.

Human cells, like all animal cells, have only a flexible plasma membrane on the outside and no rigid cell wall.

Isoenzymes, also called isozymes, are different molecular forms of an enzyme that speed up the same chemical reaction but differ in their amino acid sequence.