Heat is

Options

A. energy transferred by virtue of a temperature difference.
B. energy transferred by macroscopic work.
C. energy content of an object.
D. a temperature difference.

Answer

### Step-by-Step Solution:

1. **Understanding Heat**:
- Heat is defined as the transfer of energy from one body to another due to a temperature difference. This means that when two objects at different temperatures come into contact, energy will flow from the hotter object to the cooler one until thermal equilibrium is reached.

2. **Identifying the Correct Definition**:
- We need to find the option that correctly describes heat. The key phrase to look for is "transfer of energy" and "temperature difference".

3. **Analyzing the Options**:
- **Option 1**: "Energy transfer by virtue of a temperature difference."
- This option correctly describes heat as it mentions both energy transfer and temperature difference.
- **Option 2**: "Energy transferred by a microscopic vector."
- This option is incorrect as it does not relate to the definition of heat.
- **Option 3**: "Energy content of an object."
- This option is also incorrect because it refers to energy as content rather than transfer.
- **Option 4**: "A temperature difference."
- This option is incomplete as it does not mention the transfer of energy.

4. **Conclusion**:
- After analyzing all the options, the correct definition of heat is given in **Option 1**: "Energy transfer by virtue of a temperature difference."

### Final Answer:
- The correct answer is **Option 1**: Energy transfer by virtue of a temperature difference.