Answer:
substance A is a liquid, while substance B is a liquid or gas
First of all, as you seen the gases are noble which means that will not react with each other and in this case each gas create individual pressure.
P
= total pressure
P
= pressure of neon
P
= pressure of argon
P
= pressure of helium {which is required}
P
= P
+ P
+ P
1.25 = 0.68 + 0.35 + P
P
= 1.25 - [0.68 + 0.35] = 0.22 atm
Answer:

Explanation:
Hello,
In this case, since a change in science is widely known to be considered as a subtraction between the the final and initial values of two measured variables and is represented via Δ, here the final density is 5.43 g/mL and the initial one was 3.21 g/mL, therefore, the change in density is:

Best regards.