The opposite reciprocal of 7/21 is

-21/7 or -3 (depends on your instruction)

Explanation:

Opposite: the opposite of the current sign

if it is currently negative [-], then its opposite is positive [+]If it is currently positive [+], then its opposite is negative [-]

Reciprocal: changing the place of numerator and denominator

The reciprocal of a/b is b/a

7/21

Opposite: since it is positive, the opposite is negative

Reciprocal: since it is 7/21, we change the place, and it is 21/7=3

Opposite reciprocal of 7/21 is -21/7 or -3

I  cant see the question.

Magma is outside the volcano  and lava is inside the volcano.