A number is rational if it can be expressed as the ratio between two integers (of course the denominator can't be zero).
-1/16 is already a fraction, so it's rational.
0 can be expressed as a fraction: [tex] \frac{0}{n} [/tex] for any non-zero integer [tex] n [/tex] you like
[tex] \sqrt{2},\sqrt{3} [/tex] can't be expressed via a fraction between integers, and thus they are irrational.
