Calamine ($ZnCO_3$) is an ore of Zinc which contains 54% of zinc.

Noble metals (like gold) do not dissolve in common acids. Aqua-regia ($3$ parts $HCl + 1$ part $HNO_3$) is used to dissolve them.

A (2,8) is an inert gas. B (2,8,7) is a non-metal (gains electrons). C (2,8,2) is a metal (loses electrons).

Mercury is a pure metal, while Brass (Copper+Zinc), Bronze (Copper+Tin), and Stainless Steel (Iron+Chromium+Nickel) are alloys.

Volume $V = (2.88 \times 10^{-8})^3 \text{ cm}^3 \approx 23.9 \times 10^{-24} \text{ cm}^3$. Mass = $V \times \rho = 23.9 \times 10^{-24} \times 7.2 \approx 1.72 \times 10^{-22} \text{ g}$. Cells in $100$ grams = $100 / (1.72 \times 10^{-22}) \approx 5.8 \times 10^{23} \approx 6 \times 10^{23}$.

Most metal oxides are insoluble in water, although some alkali oxides dissolve in water to form alkalis, but generally 'most' are not soluble in water.

Magnesium is extracted from seawater through the extraction of $MgCl_2 . 6H_2O$ salts.

Brass is an alloy of copper (Cu) and zinc (Zn).

Pearl is a hard substance produced by soft-tissue organisms. Chemically, pearl is calcium carbonate ($CaCO_3$) in a microcrystalline form, which is created by the organisms through deposition in concentric layers.

German silver is an alloy of copper, zinc, and nickel. Copper, Aluminium, and Nickel are pure metals.

Iron (Fe) metal is found in hemoglobin. The red color of blood is also due to the Iron found in hemoglobin.

According to the reactivity series: Potassium > Sodium > Calcium > Magnesium ($Mg$) > Aluminium ($Al$) > Iron ($Fe$) > Copper ($Cu$). Therefore, Mg is the most reactive.

Most metals have high melting points, not low. Therefore, option (B) is incorrect.

Non-metals are bad conductors of heat and electricity (except graphite). Therefore, statement (2) is incorrect.

Nitrogen gas is used in packets of chips, etc., to prevent oxidation (preserve) of food items.

Stainless Steel = Alloy (III), Gold = Inert metal (IV), Sulphur = Non-metal (I), Magnesium = Metal (II). Therefore a-III, b-IV, c-I, d-II.

At standard temperature and pressure, Bromine (non-metal) and Mercury (metal) are in a liquid state.

The actual electronic configuration of Copper (Cu) is $[Ar] 3d^{10} 4s^1$.

Due to the property of Sonority, metals produce sound when struck, hence they are used to make bells and musical instruments.

The chemical name of Heroin is Morphine diacetate (Diacetylmorphine).