We can use combined gas laws to solve for the volume of the gas

where P - pressure, V - volume , T - temperature and k - constant

parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
T1 - temperature in Kelvin - 20 °C + 273 = 293 K
T2 - 40 °C + 273 = 313 K
substituting the values

V = 17.8 L
volume of the gas is 17.8 L
is this a cult?im confused
Answer : The mass of oxygen will be, 36.8 grams
Solution : Given,
Moles of water = 2.30 moles
Molar mass of
= 32 g/mole
First we have to calculate the moles of oxygen.
The balanced chemical reaction will be,

From the balanced reaction we conclude that
2 moles of water decomposes to give 1 mole of 
2.30 moles of water decomposes to give
moles of 
Now we have to calculate the mass of oxygen.


Therefore, the mass of oxygen will be, 36.8 grams
This should help you with your question:
Gravitational pull = 9.8 m/s^2
1/2 x 9.8 x 7^2 = 240.1 m
The rock has fallen 240.1 m.
I cannot help you with the rest, but this should give you a headstart.