State whether each set of hypotheses is valid for a statistical test. If not valid, explain why not.
(a) H₀: ρ = 0 vs H_a: ρ < 0
(b) H₀: p̂ = 0.3 vs H_a: p̂ ≠ 0.3
(c) H₀: μ₁ ≠ μ₂ vs H_a: μ₁ = μ₂
(d) H₀: p = 25 vs H_a: p ≠ 25

Determine whether the sets of hypotheses given are valid hypotheses.