Explanation:

Correct Answer is (d).Sentence I. The government is planning a new salary scale for all professors of universities run by the UP government.
The sentence above is absolutely correct as the word ‘scale’ here refers to ‘a graduated range of values forming a standard system for measuring or grading something’.
Sentence II. We cannot track them in the mortal world until they use a substantial scale of magic.
The usage of the word ‘scale’ is contextually wrong here and doesn’t make any sense. ‘Amount’ would have been a better word in place of ‘scale’ here.
Sentence III. No one could have foreseen the scale of the disaster.
The sentence with the word ‘scale’ is absolutely correct. Here, the word ‘scale’ refers to ‘the relative size, extent or magnitude of something’.
Clearly, option D is the correct answer.