Answer: The space occupied by the gas at 400 torr and
is 250 mL.
Explanation:
Given:
= 250 mL,
= 800 torr, 
,
= 400 torr, 
Formula used is as follows.

Substitute the values into above formula as follows.

Thus, we can conclude that space occupied by the gas at 400 torr and
is 250 mL.
The symbol, the atomic mass, the number of protons and electrons
I believe the answer is gills
Fish's use gills to breathe, so tadpoles should use gills too
hope this helps
(got the info from a documentary i watched a couple years ago)