General Science Previous Year Questions (PYQ) with Answers – Page 30

Of the four options, oxygen is by far the most plentiful element; it makes up about 46% of the Earth's crust by mass.

Copper in the +1 state is reduced to metal, so it is the oxidant; sulphur of Cu2S is oxidised, so it is the reductant.

Together the two resins take out every dissolved ion, which leaves demineralised water. In the cation exchange resin (written RH), metal ions such as Ca2+, Mg2+ and Na+ are swapped for H+ ions.

The stone takes 2 s to fall 20 m, and in that time it moves 12 × 2 = 24 m sideways.

The heater's resistance is 220/0.5 = 440 Ω, so at 120 V the current is 120/440, about 0.27 A. By Ohm's law, V = IR, and for an ohmic conductor at a steady temperature the resistance stays the same.

A beam seen from the side is visible only because tiny particles send some of its light sideways. Light travelling in a straight line cannot enter our eyes unless something redirects it towards us.

A leaf from a sunny day is full of starch made by photosynthesis, and iodine turns starch blue-black. This is the standard school test for starch in a leaf.

A body moving faster than sound outruns its own sound waves, which pile up into a shock wave heard on the ground as a sonic boom.

During a hard sprint the muscles run short of oxygen and switch to anaerobic respiration, which leaves lactic acid behind.

Gravitational force varies inversely as the square of the distance, so halving the distance makes the force 2 × 2 = 4 times larger.

A cell whose nucleus is well organised and bounded by a nuclear membrane is called a eukaryotic cell. The word comes from the Greek eu, meaning true, and karyon, meaning kernel or nucleus.

Carbon-14 is the radioactive isotope of carbon used for radiocarbon dating, and its half-life is close to 5,700 years, which is the figure quoted in the question.

In 1924 Satyendra Nath Bose sent Albert Einstein a paper deriving Planck s radiation law by counting indistinguishable light quanta.

Methyl ethyl ketone has a methyl group on one side of the carbonyl and an ethyl group on the other, which makes four carbons in all with the carbonyl at the second position, so its IUPAC name is butan-2-one or 2-butanone.

A homogeneous mixture has the same composition and properties throughout and no visible boundary between its parts, so a true solution such as salt water qualifies, and so does brass, an alloy of copper and zinc, since alloys are solid solutions.

Charles’s law says that at constant pressure the volume of a fixed mass of gas is directly proportional to its absolute temperature, so V by T stays constant.

None of the three substances listed slows a reaction down; the substance that does that is called a negative catalyst or an inhibitor.

Nothing is oxidised when a soda bottle is opened; the pressure inside simply falls, the dissolved carbon dioxide becomes less soluble and escapes as bubbles.

Naphthalene is an aromatic hydrocarbon, C10H8, with a very high proportion of carbon, so the air around the flame cannot supply enough oxygen to burn all of it to carbon dioxide.

Radiation carries heat as electromagnetic waves, so it needs no material medium and can travel through a vacuum. This is how the heat of the Sun crosses empty space to reach the Earth, and why you feel warmth in front of a fire without touching it.