General Science Previous Year Questions (PYQ) with Answers – Page 82

The element with atomic number 56 is barium, and its outermost electron enters the 6s orbital, so it sits in the s-block.

Relative atomic mass is measured against the carbon-12 atom, one-twelfth of whose mass is taken as the standard unit. That unit is the atomic mass unit, written u, and it is defined as exactly one-twelfth of the mass of one atom of carbon-12.

Melting of ice only changes the state of water from solid to liquid; no new substance is formed, so it is a physical change.

Ice melts at 0 degrees Celsius, and 0 degrees Celsius is 273 K on the Kelvin scale. To change Celsius into Kelvin, add 273 to the Celsius reading, so 0 + 273 gives 273 K; the melting point of ice is usually written as 273.15 K in exact work.

Mass by mass percentage of a solution is the mass of the solute divided by the mass of the whole solution, multiplied by 100.

The heat produced by a current is given by Joule's law of heating, H equals I squared into R into t. Here the current is 0.3 A, the resistance is 418 ohms and the time is 1 minute, which is 60 seconds.

A quantity that has both magnitude and direction is a vector, and momentum, which is the product of mass and velocity, is a vector because velocity has a direction.

Ammonium chloride is the salt of a strong acid, hydrochloric acid, and a weak base, ammonium hydroxide, so its aqueous solution is acidic and its pH is less than 7.

Adding water to an acid spreads the same number of hydrogen ions through a larger volume, so the number of hydrogen ions per unit volume falls, and that process is called dilution.

Birds and mammals are warm-blooded, which means they keep their body temperature nearly constant whatever the temperature outside, and a pigeon is a bird.

The weight of an object is the force with which the earth attracts it, so the force of gravity acting on an object is its weight.

Deposition is the direct change of a substance from the gaseous state to the solid state, without passing through the liquid state in between.

The receptors that pick up taste are called gustatory receptors, and they sit inside the taste buds on the tongue.

Pitch is how shrill or how flat a sound seems to the ear, and it is decided by frequency, the number of vibrations per second measured in hertz.

The first equation of motion is written as v equals u plus a t, so it tells how the velocity of a body changes with time.

The nephron is the structural and functional unit of the kidney, and each human kidney holds about one million of them.

An echo is the sound heard when a wave is reflected from a distant obstacle and comes back, so in the time measured the sound covers the distance to the cliff and then the same distance back again.

Plant tissues are first divided into meristematic tissue, whose cells keep dividing, and permanent tissue, whose cells have stopped dividing and have taken a fixed shape and job.

The middle ear holds three tiny bones, the smallest in the human body, called the malleus, the incus and the stapes, which in everyday English are the hammer, the anvil and the stirrup.

Sound is a mechanical wave: it travels only when the particles of a medium push against their neighbours, so the closer and more tightly bound those particles are, the faster the disturbance is passed on.