To retrieve the number of products with a null list price, we need to use the COUNT function in a manner that handles NULL values appropriately. The query 'SELECT COUNT(list_price) FROM product_information WHERE list_price IS NULL;' would not work as COUNT(list_price) does not include NULL values in its count. Instead, by using 'SELECT COUNT(NVL(list_price, 0)) FROM product_information WHERE list_price IS NULL;', the NVL function replaces NULL values with 0, and the WHERE clause ensures we are counting only those records where list_price is originally NULL. This way, we get the correct count of all rows where list_price is NULL.