Answer:
Molecular mass
Explanation:
Molecular formulas is the actual number of atoms of each element in the compound while empirical formulas is the simplest or reduced ratio of the elements in the compound.
Thus,
Molecular mass = n × Empirical mass
Where, n is any positive number from 1, 2, 3...
Thus if the molecular mass is known, then we can find the value of n which results to molecular formula.
The correct Answer for this question is D
Explanation:
A chemical reaction is defined as the reaction in which bonds between the reactants either break or form which leads to the formation of a new substance.
For example, 
So, when we drop a sodium metal into water then it produces a frizzing sound which shows the metal is reacting with water.
We know that when two aqueous solutions chemically react with each other then it may lead to the formation of an insoluble substance which is known as precipitate.
This means that formation of a precipitate is also a chemical reaction.
Thus, we can conclude that following are the statements which show evidence for a chemical reaction.
- Dropping sodium metal into water produces fizzing.
- Mixing two aqueous solutions produces a precipitate.
<>"One such trend is closely linked to atomic radii -- ionic radii. Neutral atoms tend to increase in size down a group and decrease across a period. When a neutral atom gains or loses an electron, creating an anion or cation, the atom's radius increases or decreases, respectively."<>