Answer:
3. Principal.
Step-by-step explanation:
For the sentence
How much is the ________ on that loan?
the correct word will be PRINCIPAL.
In this case, 'principal' means the exact initial amount that was borrowed or taken as loan from someone or somewhere else. This original amount is known as 'the principal' in a business or economic language.
The other options "principel/principle" are both wrong as-
1. Principel is not even a valid English word.
2. Principle is more like the morals and fundamental philosophical truths related to one's beliefs and behavior/reasoning.