The cyanide process, also called the Macarthur-Forrest Process, method of extracting silver and gold from their ores by dissolving them in a dilute solution of sodium cyanide or potassium cyanide. 

Hence, the correct option is (D).

Copper is mainly extracted from copper pyrites. After the concentration of its ore by the froth flotation process, the ore is roasted in a current of air to remove arsenic, antimony, and much sulphur.

The ore is then mixed with a little coke and sand and smelted in a water-jacketed blast furnace. The minor reactions that occurred during roasting continue here. Ferrous oxide combines with sand to form a fusible slag.

The slag obtained during the extraction of copper from copper pyrites is composed of FeSiO₃.

Hence, the correct option is (A).

The velocity of body just before touching the lake surface is,

Automobiles burn petroleum inefficiently causing 80% of air pollution and 75% of noise pollution in urban areas. They release hydrocarbons (13.7%), carbon monoxide (77.2%), nitrogen oxides (7.7%), sulphur oxides, ammonia, aldehydes and lead (90% of total lead poisoning). Lead is present in petroleum in the form of Pb(CH₃)₄ and Pb(C₂H₅)₄ as antiknock agent.

Hence, the correct option is (D).

Electromotive force, E.M.F = −dϕ/dt.

We know ϕ flux is the dot product of magnetic field vector and area vector.

ϕ = BA cos(θ),

If either of the three, that is, magnetic field, area, or angle changes, the E.M.F will change, flux changes due to which E.M.F can be induced.

Hence, the correct option is (D).

The inter-particle forces are strongest in NH₃ (Hydrogen bonds). In PH₃ and AsH₃ the inter-particle forces are dipole − dipole forces which are relatively stronger in AsH₃.

So, the increasing order of enthalpy of vaporization is PH₃ < AsH₃ < NH₃

Hence, the correct option is (D).

The hormone relaxin is produced in the later phase of pregnancy. It is produced by the ovary. 

Relaxin is produced by the corpus luteum present in the ovary. Ruptured Graafian follicle is called corpus luteum, which has endocrine function.

Graafian follicle is not formed when the woman is pregnant. 

Uterus and foetus do not produce relaxin.

Hence, the correct option is (C).

Option (A) is incorrect because ricin is a toxin obtained from Ricinus plant. Vinblastin and curcumin are drugs. 

Morphine and codeine are alkaloids. 

Abrin is also a toxin obtained by plant Abrus. 

Concanavalin A is a lectin.

Hence, the correct option is (A).