Can you help me understand the difference (what is wrong with) the following hypotheses?

Can you help me understand the difference (what is wrong with) the following hypotheses?

a)      H0: μ = 100 vs. Ha: μ ≠ 110

b)     H0: = 100 vs. Ha: < 100

c)      H0: = 0.50 vs. Ha: ≠ 0.50