What's wrong

Question

jeeva = "jee"
jeeva[0] = k
print(jeeva)

Answer 1

Probably you should do-
jeeva = "jee"
print(jeeva.replace('j','k'))
// It will give 'kee'.

Mistakes-
1) jeeva is a string object and is not an array in itself.
2) k is not defined.

Things to remember-
String objects are immutable and any alteration would lead to a creation of a new object.

Answer 2

you're replacing the first character in jeeva with k which is j