HI Raj, columns available to show in the BOM are based on custom properties of the parts shown in the table. So you need to go through each part model and add the property under File > Properties > Custom as pictured below.
When you save and return to the drawing, you should be able to add this extra column to the BOM as it will be detected as a property to show.
Each part needs to have this property added to give you a complete list
And note the units are based on Tools > Options > Document Properties > Units where you can set it to sq.inch