As per the the question the sound source is the mosquito.
the mosquito produces the sound with the help of its wings
as per the question the wings vibrate at the rate of 500 vibrations per second.
we have been asked to calculate the time period of vibration.
we know that that time period is the reciprocal of frequency of vibration
hence time period [T]=
![(1)/(frequency)](https://img.qammunity.org/2019/formulas/physics/middle-school/igzapvdmuwiea5to5pz31uw1fieozlv7z5.png)
=
![(1)/(f)](https://img.qammunity.org/2019/formulas/physics/middle-school/cnm34oqstx5n8lupnkwsgiyhu8rpjditnt.png)
=
![(1)/(500) second](https://img.qammunity.org/2019/formulas/physics/middle-school/1pgebynd0052mndowaq6hnv4tf1y0r9mkd.png)
=0.002 second
hence the time period of the vibration of the wings of the mosquito is 0.002 second.