Define Bulk modulus and give its SI unit.

Explanation

It is ratio of normal stress to the volume strain.
i.e. Bulk modulus (B)= `("Normal stress")/("Volume strain")=(F//A)/(-(Delta V)/(V))`
`B= -(FV)/(A Delta V)= -(PV)/(V)`
Negative sign indicates decrease in volume with increase in pressure. SI unit is N `m^(-2)`