Please explain what kind of syntax errors or problems the following statements might have.

$.$~ $=$ x ; I $/1.--$ : $-----------------------$ int X$=3\mathrm{.}0.$; $//2.\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

char ch$="$a$"$; $//3.---------------------\_$int a$==$l; II$4.\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_$

int if$=3$; $/15.\_\_\_$