The parameters of the unit cell of a substance are a = 2.5, b = 3.0, c = 4.0, $$\alpha$$ = 90$$^\circ$$, $$\beta$$ = 120$$^\circ$$, $$\gamma$$ = 90$$^\circ$$. The crystal system of the substance is :

Given below are two statements. One is labelled as Assertion A nd the other is labelled as Reason R.

Assertion A : Sharp glass edge becomes smooth on heating it upto its melting point.

Reason R : The viscosity of glass decreases on melting.

Choose the most appropriate answer from the options given below.

A hard substance melts at high temperature and is an insulator in both solid and in molten state. This solid is most likely to be a/an :

In a binary compound, atoms of element A form a hcp structure and those of element M occupy 2/3 of the tetrahedral voids of the hcp structure. The formula of the binary compound is :