The correct answer is option 3: specific heat.

Option 1, water equivalent, refers to the mass of water that would have the same heat capacity as the body. It is not the heat given to the body.

Option 2, thermal capacity, is the amount of heat energy required to raise the temperature of the body by 1 °C. This is similar to the concept mentioned in the question, but "thermal capacity" is not the commonly used term in this context.

Option 3, specific heat, is the amount of heat energy required to raise the temperature of a unit mass of the substance by 1 °C. It is a property specific to each substance and is commonly used in heat transfer calculations.

Option 4, temperature gradient, refers to the change in temperature per unit distance in a medium. It does not directly relate to the heat given to a body to raise its temperature.

So, specific heat is the correct term to describe the heat given to a body which raises its temperature by 1 °C.