If two gases with pressures of 2 atm and 3 atm are mixed at constant temperature, the total pressure will be the sum of the two pressures. Therefore the answer is D. 2 atm + 3 atm or 5 atm will be the total pressure of the gas mixture.
My opinion it would be Issac Newton
A hypothesis is a working explanation, where a theory is a well established explanation. So really hypothesis is a more of a "guess and check" "work in progress" and a theory is like a summary of overall explanation of the observed behavior. hope this helps