A base is weak when only a little of it dissolved in Water.
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Since there's specific heat, you should use Q=mc△T. Depends on if this question also involves phase change or not, you might will need Lf (latent heat of fusion) or Lv (latent heat of vaporisation).
The mass in a chemical reaction remains (mostly) the same.
(except for radiation/nuclear fission, in which mass gets converted into energy)
Answer:
77.14 atm of pressure should be of an acetylene in the tank.
Explanation:

According to reaction, 2 moles of acetylene reacts with 5 moles of oxygen.
Moles of oxygen=
Moles of acetylene =

Volume of large tank with oxygen gas, 
Pressure of the oxygen gas inside the tank = 
..[1]
Volume of small tank with acetylene gas ,
Pressure of the acetylene gas inside the tank = 
..[2]
Considering both the gases having same temperature T, [1]=[2]



77.14 atm of pressure should be of an acetylene in the tank.
In a salt solution, the water potential is lower than that in the cell. In this case, water molecules will flow from a region of higher water potential to a region of lower water potential by osmosis. Which where water molecules is now flowing out of the cell to the salt solution. Because the cell lose so much water that it now shrinks.
Osmosis is where water molecules move down the water potential gradient through a semi permeable membrane, which is the cell membrane in this case.