Chemistry Questions and Answers

Answer: C

The pair is mercury, bromine.

At room temperature, mercury is the only metal that is liquid and bromine is the only non-metal that is liquid. Mercury is used in thermometers and barometers, and bromine is a reddish-brown, fuming liquid.

Gallium is a metal that melts at about 30°C, just above room temperature, so it melts in the hand but is normally solid. Fluorine is a gas. The option bromine, mercury puts the two the wrong way round.

Answer: B

The correct pair is Bronze - Alloy.

Bronze is an alloy, chiefly of copper and tin.

The other pairs are wrong. Aluminium is a metal, not a non-metal. Steel is an alloy of iron and carbon and is not radioactive. Carbon is a solid non-metal, found as graphite and diamond, not a gas.

Answer: B

Nylon threads are made of a polyamide polymer.

Nylon is a synthetic polymer whose repeating units are joined by amide (-CO-NH-) links. Nylon-6,6, for example, is made by condensing hexamethylenediamine with adipic acid. It was the first fully synthetic fibre and is strong, elastic and resistant to wear.

Polyesters such as terylene have ester links, polyethylene is the plastic polythene, and polyvinyl polymers include PVC; none of them is nylon.

Answer: D

The gas usually filled in an electric bulb is Argon.

A filament lamp glows because its tungsten wire is heated to well over 2,000 °C. Argon, an inert gas, does not react with the hot tungsten, and its pressure slows the evaporation of the filament, so the bulb lasts longer. It is often mixed with a little nitrogen.

Oxygen would burn the filament out at once, hydrogen is flammable and conducts heat away, and carbon dioxide would react with the hot metal.

Answer: D

Carbon dating uses Carbon-14.

Carbon-14 is a radioactive isotope with a half-life of about 5,730 years. Living things take it in along with ordinary carbon; after death it decays without being replaced, so the fraction left shows how long ago the organism died. The method was developed by Willard Libby.

Carbon-12 and Carbon-13 are stable, so they do not decay and cannot measure time. Carbon-11 is radioactive but has a half-life of only about 20 minutes, far too short for dating.

Answer: A

The metal that is liquid at room temperature is Mercury.

Mercury melts at about -39 °C and boils at about 357 °C, so it stays liquid across ordinary temperatures. That is why it was used in thermometers and barometers.

Silver melts at about 962 °C, zinc at about 420 °C and cadmium at about 321 °C, so all three are solids at room temperature.

Answer: C

Baking soda is Sodium bicarbonate, NaHCO₃.

When heated, or mixed with an acid in a batter, it releases carbon dioxide, and the gas bubbles make cakes and breads rise. It is also used as an antacid and in fire extinguishers.

Sodium carbonate, Na₂CO₃, is washing soda. Calcium carbonate is limestone, chalk and marble, and sodium chloride is common salt.

Answer: C

The correct statement is that electrons are negatively charged and are present in the orbits.

In the model of the atom, the nucleus contains positively charged protons and neutral neutrons, while negatively charged electrons move in orbits (shells) around it.

Protons are positive, not negative, and electrons are outside the nucleus, not in it. Almost the entire mass of the atom is concentrated in the nucleus, so it is not distributed in the orbits.

Answer: A

The statement that is not a property of acids is acids turn red litmus to blue.

Acids turn blue litmus red. Turning red litmus blue is the test for a base (alkali), so this statement describes bases, not acids.

The other three are the textbook properties of acids: they taste sour (like citric acid in lemons), strong acids are corrosive, and acidic solutions have a pH below 7.

The pH scale runs from 0 to 14: values below 7 are acidic, 7 is neutral, and values above 7 are basic.

Answer: C

Metals can be beaten into sheets because they are malleable.

Malleability is the property of being hammered or rolled into thin sheets without breaking. Gold, silver and aluminium are highly malleable, which is how gold leaf and aluminium foil are made. It comes from metallic bonding, which lets layers of atoms slide over one another without the solid cracking.

Ductility is the related property of being drawn into wires, so 'they are ductile' names the wrong property. Many metals are hard rather than soft, and their atoms are closely packed, not loosely arranged.