Final answer:
An Individual retirement account (IRA) is the type of account that can only be opened in a cash account among the options provided.
Step-by-step explanation:
The account that can only be opened in a cash account from the options provided is C. Individual retirement account (IRA). An IRA is a long-term, tax-sheltered account, such as a traditional IRA, that allows individuals to contribute pretax income up to specific annual limits. Contributions to a traditional IRA grow tax-deferred, meaning you do not pay taxes on capital gains or dividend income until funds are withdrawn, typically at retirement. On the other hand, a Roth IRA involves contributions made after taxes, with the advantage that withdrawals at retirement are tax-free. Unlike IRAs, other accounts such as Individual TOD, Individual, and Custodial accounts can be established as either cash or margin accounts.