Zero is  the reciprocal of any number.

The reciprocal of  $\mathrm{a}$ where $\mathrm{a}\ne 0$ is _____

The reciprocal of  $\frac{1}{\mathrm{a}}$ where $\mathrm{a}\ne 0$ is _____.

The reciprocal of a positive rational number is a _____ rational number.

The reciprocal of a negative rational number is _____

Simplify and write the answer in the standard form: $\frac{4}{9}÷\frac{-5}{12}$

Simplify: $-8÷\frac{-7}{16}$

Simplify and write the answer in the standard form: $\frac{-12}{9}÷\left(-18\right)$

Simplify and write the answer in the standard form: $\frac{-1}{10}÷\frac{-8}{5}$