Which of the following is a valid mixed cell reference?

A mixed cell reference in Microsoft Excel fixes either the row or the column, but not both. This is done by placing the $ symbol before either the column letter or the row number.

• $A$1 – Absolute reference (both row and column fixed).
• A1 – Relative reference (both row and column change).
• $A1 – Mixed reference (column fixed, row relative). ✔
• $1A – Invalid cell reference.

Therefore, the correct answer is: $A1.