Step 1: Nature of Executor’s A/c.
Executor’s A/c is used to represent the legal heirs of the deceased partner to whom final dues are payable.
Step 2: Timing of opening.
This account is specifically opened only on the death of a partner, not on retirement or admission.
Step 3: Conclude.
Therefore, Executor’s A/c is opened when a partner dies.
Final Answer:
\[
\boxed{\text{On death of partner}}
\]