What are the estate tax consequences in the following independent cases involving commercial annuities?

1. H and W are married. H purchased a joint and survivorship annuity for $500,000. When H died the present value of W's annuity was $300,000.
2. Same as (a) except W died first and the value of H's remaining annuity was $250,000.
3. Same as (a) except that the annuity was paid for by W's employer.
4. Same as (b) but the policy was purchased with community property.
5. H and W each purchased a single life annuity for $250,000. H died first, several years before W.
6. How would the answers above change if the annuities involved were private annuities?