States of Matter

When ice floats in water and melts, the water level remains the same. This is because the volume of water displaced by the ice equals the volume of water produced when the ice melts. Ice is less dense than liquid water, which is why it floats.

(a branch of science concerned with). Correct word order. All the other options make use of words which makes the sentence incomplete. 

It is correct as by the time water has cooled to 4⁰C., the molecules' energy has dropped enough that they are very near each another. So each H₂O molecule forms more stable hydrogen bonds, with up to four fellow molecules. At 0⁰C, the molecules in ice are held rigidly apart. That means more empty space between molecules, so frozen water occupies more room and is less dense.

It is correct as water molecules are less dense than ice. Water expands on cooling.

This is correct. In a pure chemical compound, elements are always present in a definite proportion by mass. This is known as the law of definite proportions. In this case, if we decompose 100 grams of pure water by passing electricity through it, then we get 11 grams of hydrogen and 89 grams of oxygen, showing that hydrogen and oxygen are combined together in water in the same constant proportion of 1 : 8 by weight.

Water is used in car radiators primarily because of its high specific heat capacity (4200 J/kg°C), meaning it can absorb large amounts of heat for small temperature changes. This makes it excellent for cooling engines. While water is also easily available and has high density, these are not the primary reasons. Low boiling point would actually be a disadvantage.

Rain water is the purest form of natural water because it forms through the process of evaporation and condensation, which naturally removes most impurities. River water contains dissolved minerals and pollutants from the ground it flows over, filtered water still contains some dissolved substances, and mineral water has added minerals for taste.

Potassium has a density of about 0.862 g/cm³, which is less than water's density of 1 g/cm³. This makes potassium float on water. Sulphur (~2.07 g/cm³), iodine (~4.93 g/cm³), and copper (~8.96 g/cm³) are all denser than water and would sink.

This is the correct option. Copper sulphate pentahydrate contains 5 molecules of water of crystallisation per formula unit.

Fog is a colloidal system where liquid water droplets are dispersed in a gas (air). This makes it a 'liquid in gas' colloid. Examples include fog, mist, and sprays - where the dispersed phase is liquid and the dispersion medium is gas.

Aqua regia is the only solution that can dissolve gold. It is a mixture of concentrated nitric acid and hydrochloric acid in a 1:3 ratio, which produces reactive species that oxidize gold. Neither water nor any single acid like HCl or H2SO4 can dissolve gold.

A roof coating is a fluid applied membrane which has elastic properties that allows it to stretch and return to its original shape without damage. It provides UV protection to polyurethane foam and is widely used as part of a roof restoration system.

Diethylene glycol (DEG) is an organic compound with the formula (HOCH₂CH₂)₂O. It is a colourless, practically odourless, poisonous, and hygroscopic liquid with a sweetish taste. It is miscible in water, alcohol, ether, acetone and ethylene glycol. DEG is a widely used solvent.

An emulsion is a type of colloid where one liquid is dispersed in another immiscible liquid in droplet form, like milk fat in water or oil in water. This matches the definition of liquid in a liquid.

A dead body floats in water due to buoyancy principle - the weight of water displaced equals the weight of the body when decomposition gases accumulate, making it less dense than water. Body temperature being zero doesn't cause floating (ice floats due to crystal structure), and bodies don't lose weight after death.