Answer:
Because sodium is on the left side of the PT and phosporus is on the right side. And atomis radius decreases from left to right.
Explanation:
Answer: B. False
Explanation: A double displacement reaction is one in which exchange of ions take place. The salts which are soluble in water are designated by symbol (aq) and those which are insoluble in water and remain in solid form are represented by (s) after their chemical formulas.
Example:

Thus as we can see sodium ion
is being replaced by ammonium ions
and thus positive ions replace positive ions only and not negative ions.
Physical properties can be observed or measured without changing the composition of matter. These are properties such as mass, weight, volume, and density. Remember that density is a physical property.
Answer:
4.002602
Explanation:
the average that reflects the typical ratio of natural abundances of its isotopes.