There are four unknown compounds that are labeled w, x, y, and z. only substance y is soluble in water. compound y could be
1)iron oxide.
2)zinc hydroxide.
3)potassium bromide.
4)silver oxide.

Potassium bromide

Explanation:

Potassium bromide is an ionic compound and it is freely soluble in water as water is polar solvent (with high dielectric constant) so can easily dissolve polar or ionic compounds in it.

"Like dissolved like"

for other compounds they are not soluble in water,

Zinc hydroxide is slightly soluble in water, but very less soluble as compared to potassium bromide.

a). in this case, dh> 0 and sd> 0. if t becomes larger, the term "-tds" will become more negative. at some point, it is possible that -dts will be more negative than the dh is positive, and the reaction will become spontaneous. this is probably the correct answer, but you should look at all of the other possibilities and make sure of that.