Atomic mass of carbon is 12u and oxygen is 16u. In $CO_2$: $12 : (16 \times 2) = 12 : 32 = 3 : 8$.

Slaked lime ($ext{Ca(OH)}_2$) gives bleaching powder ($ext{CaOCl}_2$) when heated/reacted with chlorine.

Reverse Osmosis (RO) is a water purification technique used to remove ions, unwanted molecules, and large saline particles from drinking water. A semi-permeable membrane is used for this.

Distillation method is used to separate mixtures that boil without decomposing and have a significant difference between the boiling points of their components.

Gemstones like Ruby and Sapphire are formed from Aluminum oxide ($Al_2O_3$).

Explanation- A carburetor is a device that helps in mixing fuel and air together for the convenience of internal combustion inside the engine. This device passes the engine's fuel and air mixture through the intake manifold (a device that delivers air/fuel mixture to the cylinders).

According to the Mohs scale of mineral hardness, Talc is the softest mineral with a hardness of 1.

The symbol for Potassium is 'K', which is derived from the Latin word 'Kalium'.

Using the Allegation rule:
30% -- 50%
35%
(50 - 35) : (35 - 30) = 15 : 5 = 3 : 1.

Nitrogen is found at about 78% and Oxygen at about 21% in the atmosphere, which together constitute 99%.

The chemical formula of heavy water is $D_2O$ (Deuterium Oxide).

Hydrogen sulphide ($H_2S$) is an inorganic chemical compound with the molecular formula $H_2S$. It is a colorless gas that has a smell like rotten eggs. It is heavier than air, highly flammable, toxic, explosive, and corrosive.

Wood is an opaque object because it does not allow light to pass through it. Kerosene, glass, and water are transparent media.

In Portland cement, $ext{CaO}$ (Calcium oxide) is about 60-68% and $ext{SiO}_2$ (Silica) is about 17-24%.

Explanation- See the explanation of the above question.

The purest water available on Earth is rainwater because rainwater is obtained through the natural distillation process, which is the combined action of evaporation, condensation, and precipitation. Rainwater is a very dilute solution.

The chemical formula of bleaching powder is $\text{Ca(OCl)}_2$ (calcium hypochlorite). It is the main active ingredient for industrial bleaching and water treatment.

An emulsion is a mixture of two or more immiscible liquids. Oil in water (e.g., milk) and water in oil (e.g., cold cream) are both examples of emulsions.

Calcination is the process in which ore is heated in the absence or limited supply of air to obtain oxide.

The pungency in onions is due to allyl propyl disulfide and the special odor in garlic is due to allyl radical disulfide (sulfur compound).