Advisory Board .NET Developer interview questions

They have two F2F technical interview rounds. Their focus area was data structures. This is how 1st round of my interview went 1) Tell me about yourself 2) What are the frameworks in .net and their differences? 3) What is the purpose of protected internal access specifier? 4) They gave me the following program There are 2 char arrays ex: ABC, CBA. I was asked to write code to check 2 conditions i) Two char arrays should have same characters. ii) The frequency of a character in the both the arrays should be same. If both are satisfied, the function should return true otherwise false. I've proposed some solution,but they want the best and optimized one. 5) Write a SQL query to get the maximum count of employees in a department. For this they want me design the table structure and provide the best available query. 6) Difference between primary key and candidate key? I prepared for .net and got ds questions in return, so the interview didn't go well. They didn't mention anything regarding selection/rejection. They just said that they will communicate the details later.