Two words that most writers believe to be interchangeable are amount and number. However, they actually refer to two different things.
Amount refers to a quantity of something that can’t be counted, such as sand or news or jealousy. E.g., This winter we got the largest amount of snow on record.
Number refers to a quantity that can be counted, such as people or programs or bedrooms. E.g., The number of students taking my class has increased every year.
Both words are singular nouns, so that any pronoun referring to either must also be singular (“it”). In addition, the verb must agree with a singular noun (“the number is…” or “the amount was…”).