Chemistry Questions and Answers

Answer: D

Radioactivity is measured with a Geiger–Müller counter.

Radiation entering the tube ionises the gas inside; the ions are accelerated by a high potential difference and produce an avalanche that registers as a pulse. Each pulse is one detected particle, so the count rate measures the activity.

Answer: C

The nucleus contains protons and neutrons.

These are the nucleons, and they hold virtually the whole mass of the atom in a volume about \(10^{-15}\) m across. The electrons occupy the space outside the nucleus, which is why the atom as a whole is some hundred thousand times larger.

Answer: D

The group displacement law was given by Soddy and Fajans.

It states that alpha emission moves an element two groups to the left in the periodic table, while beta emission moves it one group to the right. That follows from the change in atomic number: \(-2\) for alpha, \(+1\) for beta.

Answer: C

A water molecule can form up to four hydrogen bonds.

It has two hydrogen atoms, each able to donate a bond, and two lone pairs on the oxygen, each able to accept one. This tetrahedral capacity is why ice has an open hexagonal lattice and is less dense than liquid water.

Answer: B

Butane is used in cigarette lighters.

It liquefies under modest pressure at room temperature - a few atmospheres are enough - so a large amount of fuel is stored in a small transparent reservoir, and it vaporises instantly on release. Propane would need a much stronger container.

Answer: B

The correct order is \(\mathrm{Al_2O_3 < MgO < Na_2O < K_2O}\).

Basicity of an oxide increases as the element becomes more metallic - that is, down a group and to the left across a period. \(\mathrm{Al_2O_3}\) is amphoteric, MgO weakly basic, and \(\mathrm{Na_2O}\) and \(\mathrm{K_2O}\) strongly basic, with potassium the most electropositive of the four.

Answer: D

All of these - none of the three is a metal.

Sulphur and nitrogen are non-metallic elements, and sugar is an organic compound, not an element at all. A metal is lustrous, malleable and a good conductor; none of these fits.

Answer: B

\(\mathrm{Na^+}\) has 10 electrons.

A sodium atom has 11 electrons \((2,8,1)\); losing the single 3s electron leaves \(2,8\), the neon configuration. The nucleus still holds 11 protons, which is why the ion is much smaller than the atom.

Answer: A

Nail polish remover contains acetone.

Propanone dissolves the nitrocellulose and resins of the polish quickly and evaporates at once, being volatile. It also strips the natural oils from the nail, which is why acetone-free removers use ethyl acetate instead.

Answer: A

The ozone hole is a thinning of the ozone layer in the stratosphere.

It is not a literal hole but a seasonal depletion, worst over Antarctica in the southern spring, where chlorine radicals released from CFCs destroy ozone catalytically on the surfaces of polar stratospheric clouds. One chlorine atom can destroy many thousands of ozone molecules before it is removed.