Generally (but far from universally), the elements within a group have similar characteristics. Antimony, nitrogen, and arsenic are all part of the same group as phosphorous (the pnictogens, or group 5A). Oxygen is not in this group, but rather in an adjacent group (the chalcogens, or group 6A). Thus, the answer here should be oxygen.
That said, there can be very significant differences in characteristics among the elements within a group, and that is certainly the case here. For example, free nitrogen exists predominantly as a molecular gas (N₂) and makes up about 78% of the atmosphere we breathe. Elemental arsenic (As), while in the same group as nitrogen, is naturally found in the solid state and is poisonous to humans (arsenic is sometimes included among the toxic heavy metals, although it’s technically a metalloid).
I will have to say that this statement is true
P1: 741 mmHg
V1: 3.49 L P1 x V1 / P2= (741 mmHg) (3.49 L) / 760 mmHg = 3.40 L
P2: 760 mmHg
V2: ? L
1 mole = 6.22 x 10^23 molecules (Avogadro's number)
15 moles x (6.22 x 10^23) = 9.33 x 10^24 atoms
In order to calculate the number of atoms, we must first know the number of moles present. And
moles = (mass present) / (molecular mass)
Therefore, the moles of Mg present are
170 / 24 = 7.08
The number of atoms in a mole of substance is given by Avagadro's Number which is 6.02 x 10^23
Since there are 7.08 moles, there are:
7.08 * 6.02*10^23
= 4.26 * 10^24 atoms
