States of Matter

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.

Quinoline is a heterocyclic aromatic organic compound. It is a colourless hygroscopic liquid with a strong odour. Quinoline is slightly soluble in cold water but dissolves readily in hot water and most organic solvents.

This is the correct answer. 

The Mpemba effect is the observation that warmer water sometimes freezes faster than colder water. Although the observation has been verified, there is no single scientific explanation for the effect.

The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid.

A supersolid is a spatially ordered material with superfluid properties. Superfluidity is a special quantum state of matter in which a substance flows with zero viscosity.

A foam is a substance that is formed by trapping many gaseous bubbles in a liquid or solid. A foam is normally an extremely complex system consisting of polydisperse gas bubbles separated by draining films.

Nanofoams are a class of nanostructured, porous materials, foams, containing a significant population of pores with diameters less than 100 nm. Aerogel is an example of nanofoam.