Question

What are the factors that affect the efficiency of lookup operations in a hash table?

Answer 1

There are number of factors that effect the efficiency of lookup operation in a hash table . 
One the important factor is the quality of hash function.
Also the number element stored in the hash table effect the overall efficiency of the lookup operations,
Moreover, number of buckets in the hash table also effects in this regard.

Hash table  is actually a data structure which usually for implementing 'associative array abstract data type".

Hope this will help you.