The digestion system starts in the mouth ( physical digestion) ........
I believe it would be the 2nd one, “increasing the area of their contact”.
Answer:
A is Mg^2+
B is K^+
C is Se^2-
D is Cl^-
Ca^2+ lies between Mg^2+ and K^+
S^2- lies between K^+ and Se^2-
Explanation:
I have attached an image of the four spheres.
Remember that, cations are smaller in size than the corresponding atom atom because the formation of a cation often involves the removal of an entire shell. Anions are larger in size than the corresponding atom because an electron is added thereby expanding the electron cloud and size of the anion.
From left to right let us designate the spheres as ABCD.
A is Mg^2+
B is K^+
C is Se^2-
D is Cl^-
Ca^2+ lies between Mg^2+ and K^+
S^2- lies between K^+ and Se^2-
Endothermic is a chemical reaction which absorbs energy in the form of heat
Answer: The pressure of the gas is 19 atm.
Explanation: By using ideal gas equation, which is:

Given conditions are:
T = 20°C = (273 + 20)K = 293K
V = 5 gallon = ( 5 × 3.97)L = 18.95L
n = 15 moles
(Gas Constant)
P = ? atm
Putting all the values in above equation, we get

P = 19 atm
Therefore, the pressure of the gas is found to be 19 atm.