Assertion (A): Combustion of all organic compounds is an exothermic reaction.

Reason (R) : The enthalpies of all elements in their standard state are zero.

(i) Both A and R are true and R is the correct explanation of A.

(ii) Both A and R are true but R is not the correct explanation of A.

(iii) A is true but R is false.

(iv) A is false but R is true.

HCP crystal is made of A ions and B ions are arranged in 2/3rd of octahedral voids. The simplest formula of compound is :-

Which of the following is a carbonate ore ?

Which of the following complex is paramagnetic, inner orbital complex and coloured :-

The orbital angular momentum of 3d electron is

For the reaction, CaCO₃(s) → CaO(s) + CO₂(g) △H = 82.8 kJ at 25°C, △U at 25°C is