General Science GK Questions with Answers – Page 27

Borax is sodium tetraborate decahydrate, Na2B4O7·10H2O, so it contains only sodium, boron, oxygen and hydrogen. Its chemical name is sodium tetraborate, and the ten molecules of water of crystallisation supply the hydrogen and part of the oxygen.

When ice melts it only changes from solid to liquid; the substance is still water, so it is a physical change.

Ribosomes make proteins, a job every living cell must do, so they are present in both prokaryotic and eukaryotic cells.

Railway tracks are joined by the thermite process, in which aluminium powder reduces iron oxide to molten iron. The reaction is Fe₂O₃ + 2Al → 2Fe + Al₂O₃.

The element with atomic number 11 is sodium, and with one electron in its outermost shell its valency is 1.

The force gives the car an extra 15 m/s, which is 54 km/h, and 40 + 54 = 94 km/h. By Newton's second law, acceleration a = F/m = 1000 N ÷ 800 kg = 1.25 m/s².

The human eye responds only to visible light, which lies roughly between 400 nm (violet) and 700 nm (red), and 500 nm is the only one of the three values in that range.

A photographer's flash tube is filled with xenon, which gives an intense burst of white light when a high-voltage spark passes through it.

Liquid nitrogen boils at about −196 °C, cold enough to stop almost all biological activity, and it is cheap, inert and safe to handle.

Rutherford's model could not explain why the orbiting electrons do not fall into the nucleus. According to classical physics, a charged particle moving in a circular path is accelerating and must keep radiating energy.

Several groups of ants, above all the leafcutter ants of the Americas, grow fungus as their food, a form of farming that began millions of years before human agriculture.

Ferric chloride is a salt of a weak base, iron(III) hydroxide, and a strong acid, hydrochloric acid, so its solution is acidic and has a pH below 7.

The magnetic field inside a long solenoid is B = μ₀nI, where n is the number of turns per unit length and I is the current, so the field depends on these two and not on the diameter.

Electromagnetic waves need no medium, so they travel through vacuum, and they consist of electric and magnetic fields that oscillate at right angles to each other and to the direction of travel.

In many single-celled organisms such as Amoeba and Paramecium, a special contractile vacuole collects excess water and some wastes from the cytoplasm and pumps them out of the cell.

A pollen grain lands on the stigma, grows a pollen tube that travels down through the style, and enters the ovary to reach an ovule, where fertilisation takes place.

A generator, whether AC or DC, produces electricity because a coil rotating in a magnetic field has a changing magnetic flux through it, and Faraday's laws say that a changing flux induces an electromotive force.

Autotrophs take carbon dioxide from their surroundings and build their own organic food from it, so CO₂ is their main source of carbon.

Soap in water forms a lyotropic liquid crystal, a phase whose ordered structure appears because of the amount of solvent mixed in, not because of temperature alone.

There is no compound with the formula 4CaO·SiO₂ in Portland cement; the four main compounds of cement clinker are dicalcium silicate, tricalcium silicate, tricalcium aluminate and tetracalcium aluminoferrite.