The equivalent rational number of $\frac{-7}{9}$ is

Equivalent rational number : If  $\frac{p}{q}$ is a rational number and for any $m\ne 0$, then $\frac{p}{q}=\frac{p\times m}{q\times m}$ here $\frac{p}{q},\frac{p\times m}{q\times m}$ are called Equivalent rational numbers.

Option ( B ) : $\frac{-63}{81}$

$\frac{-63}{81}=\frac{-7\times 9}{9\times 9}=\frac{-7}{9}$

$\therefore$ $\frac{-63}{81}$ it is a equivalent rational number of $\frac{-7}{9}$ 

Option ( A ) :  $\frac{-21}{18}$

$\frac{-21}{18}=\frac{-7\times 3}{6\times 3}=\frac{-7}{6}$ 

$\therefore$ $\frac{-21}{18}$ it is not a equivalent rational number of $\frac{-7}{9}$

Option ( C ) :  $\frac{-14}{9}$

$\frac{-14}{9}=\frac{-2\times 7}{3\times 3}$       ( when they have no common divisor)

$\therefore \frac{-14}{9}$ it is not a equivalent rational number of $\frac{-7}{9}$ 

Option  ( D ) : $\frac{-49}{81}$ 

$\frac{-49}{81}=\frac{-7\times 7}{9\times 9}$       ( when they have no common divisor)

$\therefore \frac{-49}{81}$  it is not a equivalent rational number of $\frac{-7}{9}$