$a$. You must know the difference between a solid and a gas

$b$. If a substance does not contain hydrogen, then it must not be an acid.

$c$. If we put some litmus paper in a solution and it turns red, the solution must be an acid.

$d$. If we add a substance to a red-cabbage solution and it stays red, then the substance can't be an alkal.

$e$. If we add a substance to a red-cabbage solution and it turns green, then the substance must be an alkali.

$f$. If we put some litmus paper in a solution and it turns red, then we are sure that the solution can't be an alkali.

$g$. If it's not an acid, or an alkali, then it's must be neutral.

$h$.  If we use a universal indicator to check a substance, and it turns purple, then the substance can't be an acid.