According to IRS definitions, what does not qualify as "cash"?

The correct response is that personal checks do not qualify as "cash" according to IRS definitions. In the context of taxation and financial reporting, the IRS typically defines "cash" to include physical forms like currency and coins, and also monetary instruments that are readily convertible to cash, such as cash equivalents and foreign currency.

Personal checks, while often used for transactions similarly to cash, are not immediately liquid. They require processing and may not be guaranteed funds until they have been cleared by the bank. This processing time and uncertainty about the availability of funds distinguish personal checks from cash.

On the other hand, cash equivalents refer to short-term, highly liquid investments that are easily convertible to cash and are considered near cash in financial transactions. Currency and coins obviously represent cash in its most direct form, and foreign currency, while it may represent different denominations and value, is still classified as cash since it can be exchanged for goods and services or converted into domestic currency. Thus, these forms are treated under the IRS guidelines as cash.