Which statement or statements regarding the chi-squared distribution (χ ²) is correct?

1. The chi-squared distribution is a distribution of the sum of the squares of n independent standard normal random variables at n degrees of freedom.
2. The area under the chi-squared distribution is 1.
3. The chi-squared distribution is not used to compare observed frequency distributions with expected or theoretical distributions.
4. The chi-squared distribution cannot be used for hypothesis testing.
5. As the degrees of freedom increase, the chi-squared distribution becomes increasingly less similar to a normal distribution.