When i execute the pogram it is always showing "a"

In line 6 you are adding the array marks to the number sum. That doesn’t make much sense and you end up with sum being a string that is greater than all the numbers you compare it to.

And keep an eye on indentation to make clear that sum is calculated inside the for loop:

for (let mark of marks)
    sum += mark;

thank you for the help

a is not in any condition statement, so it will be always be executed

That’s just wrong. There are four conditional returns above it so it will only be executed if all four conditions are false.

You could have used else return a;

Of course but why should we add unnecessary code that doesn’t change the outcome?

I don’t know how to convince you but it’s not unnecessary. Just use “else return ‘a’;”

Adding the ‘else’ will work but it’s not needed.
If the 4 if statements are false ‘return a’ is always executed.

Yeah, I now get it, you’re right