Final answer:
The formula not written correctly is A) SrOH2. The correct chemical formula for strontium hydroxide is Sr(OH)2, as strontium has a 2+ ionic charge and requires two hydroxide ions to balance it.
Step-by-step explanation:
A student has asked which of the following formulas is NOT written correctly. The choices were A) SrOH2 B) Al2O3 C) BaCO3 D) AgNO3. After evaluating each option, it is clear that the formula that is not written correctly is A) SrOH2.
The correct formula for strontium hydroxide should be Sr(OH)2 because strontium is a group 2 element which forms a 2+ ionic charge, thus requiring two hydroxide ions (OH-) to balance out the charge, resulting in Sr(OH)2. The other formulas B) Al2O3, C) BaCO3, and D) AgNO3 are written correctly according to the conventional rules for writing chemical formulas for ionic compounds.