You can assign custom values to droplist, and multiple-choice questions, and use those to keep track of scores. For example below we have inserted an image, with a question below it, and for the options assigned "1" as the value for answer "A" which is the correct answer, and no score for the others.
Then when we receive the results, and export to excel, we can see a 1 for each correct answer, and a zero for each incorrect answer to tally the total score per submission in excel.
If preferred, we can also automatically pass the "total" score on submission by adding a hidden text field onto the form, and then using calculated fields to tally the scores and populate that hidden field like below:
Here we are adding the text field onto the form for the purpose of storing the "Total Score", and setting it to be hidden:
Here we are using calculated fields to set this "Total Score" field to automatically tally the scores from the forms questions: