If I mix 7mL of a 0.1M solution of Ni with 3mL of a 0.1M solution of Co, what will be the final concentration of each, Ni and Co?

i'm assuming that the correct answer is indeed the first one/ "a"..

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.