The value of $\sqrt{1+1}$ is.......

For two positive integers $a$ and $b$,if $\text{HCF}(a, b) = 7$ and $\text{LCM}(a, b) = 385$,then which of the following is true?

For any positive integer $n$,the last digit of $5^n$ is always . . . . . . .

The value of $\sqrt{1+1}$ is . . . . . . (Rational,Irrational,Integer).

If $\alpha, \beta$,and $\gamma$ are the zeros of the cubic polynomial $p(x) = ax^3 + bx^2 + cx + d$ where $a \neq 0$,then the product of its zeros $(\alpha \beta \gamma)$ is:

Find the $HCF$ of $12$,$15$,and $21$.