What is the formula for calculating equivalent weight?

The choice indicating that equivalent weight is calculated by dividing molecular weight by valence is correct. In the context of chemistry, the equivalent weight of a substance is the mass of that substance that can combine with or displace one mole of hydrogen atoms or 8 grams of oxygen atoms. To find this value, you take the molecular weight of the substance, which is the weight of one mole of that substance in grams, and divide it by its valence, which represents the number of moles of hydrogen atoms that can be displaced or reacted with.

This method provides a straightforward way to assess the reactive capacity of a compound in chemical reactions and helps in stoichiometric calculations. The valence value is crucial since it reflects how the substance behaves chemically, particularly in acid-base reactions or redox processes. Thus, using molecular weight divided by valence yields the correct calculation for equivalent weight.