The following are some statements about the characteristics of covalent compounds
i) The combination of a metal and non-metal must give a covalent compound.
ii) All covalent substances are bad conductors of electricity.
iii) All covalent substances are gases at room temperature.
The correct combination is

(i) Metal + Nonmetal $\to$ Covalent bond false because They form ionic bond.
(ii) covalent substances - bad conductor false because Graphite is a good conductor of electricity.
(iii) All covalent substances - Gases at room temperature false because Many covalent substances are solids or liquids. Diamond, Graphite, ethyl alcohol, Benzene etc are not gases.

Hence, correct option is: (C) only ii and iii are correct.