Main ingredients of plastic bags and natural resources used

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

What is the formula of the ionic compound composed of calcium cations and chloride anions

Water is a highly important natural resource. which of these would be the best method to conserve water? a) drinking bottled water b) monitoring the ph of rivers c) treating and re-using wastewater d) testing nitrate levels in groundwater