**Hint:** In the given question, we have been given a number \[1 - i\] and we have to find its additive inverse. For finding that, we do not need to do any complicated stuff about the properties of the number given or any such thing, we just need to know what an additive inverse is.

**Complete step-by-step answer:**

The additive inverse of a number or expression is that number or expression which when added to that original quantity gives zero. Hence, the additive inverse of a number or expression \[k\] is given by,

Additive inverse \[ = - \left( k \right) = - k\]

**Thus, the additive inverse of \[1 - i\] is \[ - \left( {1 - i} \right) = - 1 + i\].**

**Note:** So, for solving questions of such type, we first write what has been given to us. Then we write down what we have to find. Then we think about the concept or formula which contains the known and the unknown and pick the one which is the most suitable and the most effective for finding the answer of the given question. Then we use the results or finding of the concept and apply it to our question. It is really important to know and follow all the results of the concepts if we have to solve the question correctly, as one slightest error gives the incorrect result.