General Science Previous Year Questions (PYQ) with Answers – Page 79

Anhydrous sodium carbonate is Na₂CO₃, and 2 × 23 + 12 + 3 × 16 = 106 u. Formula mass is the sum of the atomic masses of all the atoms in one formula unit of an ionic compound.

An object denser than the liquid sinks, and one less dense than the liquid floats. By Archimedes' principle, a body placed in a liquid feels an upward buoyant force equal to the weight of the liquid it displaces.

Milk is a colloid in which tiny droplets of fat are dispersed in water, so it is not uniform at the microscopic level and counts as a heterogeneous mixture.

Insulin is a protein (peptide) hormone made in the human body by the beta cells of the islets of Langerhans in the pancreas.

In photosynthesis, green plants take carbon dioxide from the air and combine it with water, using sunlight, to make carbohydrates such as glucose.

This statement is wrong: the gravitational force between two bodies depends on their masses and on the distance between them.

Three parts of oxygen-16 and one part of oxygen-18 give an average of (3 × 16 + 1 × 18) ÷ 4 = 66 ÷ 4 = 16.5 u. Isotopes are atoms of the same element with the same atomic number but different mass numbers, because they have different numbers…

The element with atomic number 8 is oxygen, which gains two electrons to complete its octet and forms sodium oxide, Na₂O. Oxygen's electrons are arranged as 2, 6, so it needs two more to reach the stable arrangement 2, 8 of neon.

A kelvin and a degree Celsius are the same size, but the Kelvin scale starts at absolute zero, which is −273.15 °C. The kelvin is the SI unit of temperature.

Hydrogen, nitrogen, oxygen and carbon dioxide all exist as gases at about 25 °C and normal atmospheric pressure. Hydrogen boils at about −253 °C, nitrogen at −196 °C and oxygen at −183 °C, so all three are gases at room temperature.

Lipases split fats into fatty acids and glycerol. Fat digestion happens mainly in the small intestine.

A muscle contracts when calcium ions are released from the sarcoplasmic reticulum, and it relaxes when they are pumped back into it.

Red blood cells far outnumber both platelets and white blood cells. A microlitre of healthy adult blood holds about 4.5 to 5.5 million red blood cells, about 1.5 to 4.5 lakh platelets and only about 4,000 to 11,000 white blood cells.

Inertia depends only on mass, and a cricket ball is the heaviest of the four. Inertia is the tendency of a body to stay at rest or keep moving uniformly in a straight line unless a force acts on it; this is Newton's first law.

Infectious jaundice, caused mainly by the hepatitis A and hepatitis E viruses, spreads through water and food contaminated with faeces.

In a uniform field the two poles of the magnet feel equal and opposite forces, which cancel each other.

Argon is an inert gas, so it does not react with the white-hot tungsten filament and slows its evaporation, which makes the bulb last longer.

Magnesium is above hydrogen in the reactivity series, so it displaces hydrogen from the acid: Mg + 2HCl → MgCl2 + H2.

The equation v = u + at has the form y = c + mx, so the graph is a straight line that cuts the velocity axis at u and has slope a. On a velocity-time graph, time is on the x-axis and velocity on the y-axis.

The apical meristem at the tip of the stem and root makes new cells that increase the plant's length, so damage to it stops growth in length.