Which process is used to convert zinc carbonate ore into zinc oxide before reduction?

The correct option is Heating strongly in limited air.

Understanding the Ore and the Process:
Zinc carbonate (ZnCO₃), commonly known as calamine, is a carbonate ore. Carbonate ores are converted into metal oxides by a process called calcination.

What is Calcination?
Calcination involves heating the carbonate ore strongly in the absence of air or in a limited supply of air. Heating causes the carbonate to decompose thermally into a solid metal oxide and gaseous carbon dioxide.

Chemical Equation:
The chemical reaction occurring during this process can be represented as:
$${\mathrm{ZnCO}}_3\left(s\right)\stackrel{\text{Heat}}{\to }\mathrm{ZnO}\left(s\right)+{\mathrm{CO}}_2\left(g\right)$$

Distinction from Roasting:
It is important to distinguish calcination from roasting. Roasting is used for sulfide ores (such as zinc blende, ZnS) and involves heating the ore strongly in the presence of excess air to convert it to oxide. Since zinc carbonate already contains oxygen in its structure, excess air is not required to oxidize it, and heating in limited air (calcination) is the appropriate method.