To get the number of different types of awards that have been won, you should use the formula COUNTD({Award}). This formula will return the count of distinct values in the Award field, which are the different types of awards that have been won.
The other options are not correct for this scenario. COVAR({Award}) is not a valid function in Tableau.
MAX({Award}) will return the maximum value in the Award field, which may not be a type of award.
INDEX() will return the index or rank of each row in a partition, which is not related to the types of awards.
References: https://help.tableau.com/current/pro/desktop/en-us/functions_functions_aggregate.htm#COUNTD
https://help.tableau.com/current/pro/desktop/en-us/functions_functions_tablecalculation.htm#INDEX The COUNTD function in Tableau calculates the number of distinct (unique) items in a field. When looking to get the number of different types of awards that have been won, the COUNTD([Award]) function will count each unique award name only once, regardless of how many times it appears in the dataset. This will return the total number of unique award types.