Crystals of a chemical in a lab slowly disappear from their container they do not become liquid. what change of state is this an example of?

The change of state that has been given in the question is called sublimation. It is actually the process in which a solid gets directly converted to gas without changing into liquid. I hope that this is the answer that you were looking for and the answer has actually come to your desired help.

d. 145 minutes

Half-life is the time needed for a radioactive to decay half of its weight. The formula to find the half-life would be:

Nt= N0 (1/2)^ t/h

Nt= the final mass
N0= the initial mass
t= time passed
h= half-life

If 25.0% of the compound decomposes that means the final mass would be 75% of initial mass. Then the half-live for the compound would be:
Nt= N0 (1/2)^ t/h
75%= 100% * (1/2)^ (60min/h)
3/4= 1/2^(60min/h)
log2 3/4 = log2 1/2^(60min/h)
0.41503749928 = -60min/h
h= -60 min / 0.41503749928= 144.6min