I believe it's alkali metals and alkaline earth metals.
Avagadro's law gives the relationship between volume of gas and number of moles of the gas. When the temperature and pressure are constant, volume is directly proportional to number of moles of gas.

V -volume and n - number of moles of gas.
parameters for the first instance are on the left side and parameters for the second instance are on the right side of the equation
initial number of moles n1 - N
n2 - 2N as the number of moles are doubled
V1 - initial volume - 2.10 L
V2 - final volume - V
substituting the values in the equation

V = 4.20 L
final volume is 4.20 L
Answer:
ii. < iv. < i. < iii.
Explanation:
Hello,
At first, the entropy is lower in solid-phase systems since their particles are molecularly closer. Next, by knowing that the higher the temperature, the higher the entropy, the gaseous HCl at 25 ºC occupies the second place. After that, it is clear 2 moles of HCl have more entropy than just 1 since the larger the amount of mater the higher the entropy.
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Answer: the boiling point elevation constant is 
Explanation:
Elevation in boiling point is given by:

= Elevation in boling point
i= vant hoff factor = 1 (for non electrolyte)
=boiling point constant = ?
m= molality

Weight of solvent (diethylether)= 330 g = 0.33 kg
Molar mass of solute (benzophenone)= 182 g/mol
Mass of solute (benzophenone) = 38.2 g


Thus the boiling point elevation constant is 
Answer:
D.atom 2 is not the same , because the mass number is different from atoms 1 and 2