Atomic mass platinum = <span>195.084 a.m.u
195.084 g -------------- 6.02x10</span>²³ atoms
?? g -------------------- 5.22x10²¹ atoms
( 5.22x10²¹) x 195.084 / 6.02x10²³ => 1.691 g
hope this helps!
13.5g H2O = 13.5/(2+16) = 0.75 mol H2O
Since for every O2 you can form 2 H2O, 0.75/2 = 0.375 mol of O2 will be needed to form 0.75 mol of H2O.
Converting from moles to molecules:
0.375 mol * 6.022 * 10^23 = 2.26 * 10 ^23 molecules
Formula Calcium chroride:

hope this helps!.
Answer:
Volume of the helium will be 1.0L
Explanation:
To understand this question it is necessary to talk about 2 laws:
Charles's law that states: The volume of a given amount of gas held at constant pressure is directly proportional to absolute temperature.
Boyle's law that states: The volume of a given amount of gas held at constant temperature varies inversely with the applied pressure when the temperature and mass are constant.
Now, in the problem, if you have 4.0L of helium:
If the temperature is halved and the volume varies directly with temperature (Charles's law), the volume of helium will be 2.0L
Then, the pressure es doubled and as volume varies inversely with pressure (Boyle's law), the volume of helium will be halved, being 1.0L.
Thus, <em>volume of the helium will be 1.0L</em>