Writing and Naming Chemical Formulas

Magnesium (Mg) has a 2+ charge, and the nitrite ion (NO2) has a 1- charge. To balance the charges, you need two nitrite ions for every one magnesium ion, resulting in Mg(NO2)2.

NH3 is the chemical formula for ammonia, a common household chemical compound.

The prefix 'tetra-' means four and 'hepta-' means seven. Therefore, tetranitrogen heptoxide corresponds to N4O7.

Ca3P2 is an ionic compound. Since calcium always forms a 2+ ion, we do not need Roman numerals in the name. It is simply calcium phosphide.

Magnesium (Mg) has a 2+ charge, and the nitrite ion (NO2) has a 1- charge. To balance the charges, you need two nitrite ions for every one magnesium ion, resulting in Mg(NO2)2.

CH4 is the chemical formula for methane, the simplest alkane and the primary component of natural gas.

Calcium (Ca) has a 2+ charge and carbonate (CO3) has a 2- charge. They combine in a 1:1 ratio to form CaCO3.

Ammonium (NH4) has a 1+ charge and carbonate (CO3) has a 2- charge. Two ammonium ions are needed to balance one carbonate ion, resulting in (NH4)2CO3.

H3PO4 is a common polyprotic acid. The anion PO4(3-) is phosphate, so the acid is named phosphoric acid.

Lead (II) indicates a Pb(2+) ion. Fluoride is F(1-). To balance the charges, two fluoride ions are required for each lead ion, resulting in PbF2.

Sr is strontium and OH is the hydroxide polyatomic ion. Since strontium is in group 2, it forms a 2+ ion, and the formula is Sr(OH)2.

Hydrofluoric acid is a solution of hydrogen fluoride in water, represented by the chemical formula HF. The other options represent incorrect stoichiometric combinations or non-existent compounds.