The correct passive form of the given sentence is:

☀ The money was stolen by an employee of the bank.

Let's break down the options:

1. The money was stolen by an employee of the bank. (Correct) This sentence correctly uses the passive voice and conveys the same meaning as the original sentence.

2. The money has been stolen by an employee of the bank. (Incorrect) This option uses the present perfect tense "has been stolen," which implies that the stealing happened in the past and has relevance to the present. The original sentence is in the simple past tense, so option 1 better reflects the intended meaning.

3. The money has been stolen by an employee of the bank. (Incorrect) This option is identical to option 2 and repeats the same sentence.

4. The money were stolen by an employee of the bank. (Incorrect) This option uses "were stolen," which is incorrect because "money" is singular, and the correct form should be "was stolen" (singular) as shown in option 1.