C. =INDEX(SORT(UNIQUE(A:A), , -1), 2) is the correct formula to find the second highest unique value in column A of your MS Excel data.
Here's why each option works (or doesn't):
A. =LARGE(A:A, 2): This formula uses the LARGE function, which returns the nth largest value in a range. However, it doesn't consider uniqueness. So, if there are duplicates of the highest value, it might not be the second truly unique highest value.
B. =LARGE(UNIQUE(A:A), 2): This formula is on the right track! It uses UNIQUE to remove duplicates and then LARGE to find the second largest value within the unique list. However, there's a simpler way.
C. =INDEX(SORT(UNIQUE(A:A), , -1), 2): This is the champion! It breaks down like this:
UNIQUE(A:A) removes duplicates from column A.
SORT(..., , -1) sorts the unique values in descending order (largest to smallest) because -1 indicates descending order.
INDEX(...) picks the value at a specific position (the second one in this case, indicated by 2).
D. =SMALL(UNIQUE(A:A), 2): This formula uses SMALL which finds the nth smallest value. We need the highest unique value, not the smallest, so this isn't the answer.
Therefore, formula C efficiently combines removing duplicates, sorting, and selecting the second largest value in a single expression.