Step 1: Set up a quantum number table.
For each decay, list the baryon number $B$, lepton number $L$, strangeness $S$ and charge $Q$ on both sides. A decay through the strong or electromagnetic interaction must keep $B$, $L$, $S$ and $Q$ all exactly equal on both sides; a weak decay must still conserve $B$, $L$ and $Q$, but is allowed to change $S$ by exactly one unit. Any decay also needs the parent's rest mass to be at least as large as the sum of the daughters' rest masses.
Step 2: Statement (A), $\mu^+ \to e^+ + \nu_e + \bar\nu_\mu$.
Lepton numbers: the muon side carries muon lepton number $L_\mu = -1$ (since it's an antimuon) and electron lepton number $L_e = 0$; the products carry $L_e = -1 + 1 = 0$ (positron plus electron neutrino) and $L_\mu = -1$ (from the muon antineutrino). Both totals match, so lepton number is conserved separately in each flavor. Charge, energy and momentum all check out too. CPT is a general theorem that holds for any Lorentz-invariant local field theory, and nothing in this bookkeeping breaks it, so this decay does not violate CPT. Statement (A) fails.
Step 3: Statement (B), $\Lambda \to p^+ + \pi^-$.
$B$: $1 \to 1 + 0 = 1$ (conserved). $Q$: $0 \to 1 + (-1) = 0$ (conserved). $S$: $-1 \to 0 + 0 = 0$, a change of one unit. Since this is a weak process (matching the $\Lambda$'s known lifetime scale) and weak decays are allowed exactly this one-unit change in $S$, the decay proceeds and strangeness is indeed violated by it. Statement (B) holds up.
Step 4: Statement (C), $p^+ \to e^+ + \gamma$.
$B$: $1 \to 0 + 0 = 0$. This mismatch alone rules the decay out completely, regardless of any other quantum number, since baryon number must be conserved in every known interaction. Statement (C) fails.
Step 5: Statement (D), $\Omega^- \to \Xi^0 + K^-$.
Every quantum number matches: $Q: -1 \to 0+(-1)=-1$, $B: 1\to 1+0=1$, $S: -3 \to -2+(-1) = -3$. So this table alone would suggest the decay is fine. But quantum numbers matching is only a necessary condition, not a sufficient one; energy bookkeeping also has to work. Adding the masses of $\Xi^0$ (about $1315$ MeV) and $K^-$ (about $494$ MeV) gives about $1809$ MeV, which is more than the $\Omega^-$ mass of about $1672$ MeV. The parent is lighter than what the decay would need to produce, so it cannot happen. Statement (D) fails.
Final Answer:
Statement (B) is the only one that survives every check.\[ \boxed{\text{(B)}} \]