Homework Q about finding the sulfide of a metal

[Isabel Day 1D]

Question E.15 asks to find the molar mass of the sulfide of M(OH)2, but I don’t understand how to derive a sulfide from this molecule and I’m confused by the wording. First, is sulfide just sulfur attached to a molecule? Second, is the metal the question asks about represented by M in the given molecule? If so, does the letter “M” always represent a metal?

[Andrew Jang 4D]

This question requires you to identify the unknown metal M in the metal hydroxide M(OH)2. Subtracting the mass of the (OH)2 part from the total mass given leaves you with a value of about 40.1 g as the molar mass of M. You can find that Ca has a molar mass of about 40.1 g, and its sulfide, CaS, has a molar mass of 72.15 g.
Sulfide is an anion of sulfur S2- so the sulfide of Ca would be CaS. As for M representing metals, I’m not sure if it will always represent metals but you can assume it in the context of this problem.

[Alan Huang 1E]

In general, sulfide would be sulfur with another metal, and you can find the sulfide of a metal by comparing charges and putting them together.