In how many ways can $10$ true-false questions be replied?

How many $3$-digit even numbers can be formed using the digits $0, 2, 3, 5, 7$ when repetition is not allowed?

$A$ polygon has $35$ diagonals; then the number of its sides is:

The number of ways in which the following prizes can be given to a class of $20$ boys,first and second Mathematics,first and second Physics,first Chemistry,and first English is:

Six '$X$'s have to be placed in the squares of the figure such that each row contains at least one '$X$'. In how many different ways can this be done?

$A$ code word is to consist of $2$ English alphabets followed by $2$ distinct numbers between $1$ and $9$. For example,$CA23$ is a code word. How many such code words are there?