Step 1: Fix what is given and what follows from it:
A has Home and C has Finance. Since A holds a portfolio, E must also hold one (E insists on a portfolio if A gets one). So A, C and E are in.
Five people must be appointed, so exactly two more come from B, D and F. D and F cannot both be in, because F does not want a portfolio if D gets one.
So the two extra people are either B and D, or B and F. In both cases B is in, and exactly one of D, F is in.
Step 2: The three portfolios left:
Power, Defence and Telecom are left for E, B and one of D or F. We need the option that cannot be completed in a valid way.
Step 3: Check option (1): D-Defence, B-Telecom:
E must take Power. So A-Home, C-Finance, D-Defence, B-Telecom, E-Power, with F out.
D holds Defence, so B's rule about Power or Telecom is not triggered. F is out as required. This is valid.
Step 4: Check option (2): F-Defence, B-Telecom:
E must take Power. So A-Home, C-Finance, F-Defence, B-Telecom, E-Power, with D out.
D is out, so F may be in. Nothing is broken. This is valid.
Step 5: Check option (3): B-Defence, E-Telecom:
Power goes to D or F. If D took Power, B would have to take Telecom, but E has it, so that fails. If F takes Power, then D is out and everything is fine: A-Home, C-Finance, B-Defence, E-Telecom, F-Power.
One valid completion exists, so this option can be a valid assignment.
Step 6: Check option (4): B-Defence, D-Telecom:
D holds Telecom, so B must hold Power. But B already holds Defence, so B cannot hold Power. B's condition is broken.
Changing the remaining slot does not help, because the problem is already in the two portfolios given. So this assignment can never be valid.
Final Answer:
Option (4) is the one that is NOT a valid assignment.
\[ \boxed{\text{Option 4}} \]