<u>Explanation:</u>
Molecular formula is the chemical formula which depicts the actual number of atoms of each element present in the compound.
Empirical formula is the simplest chemical formula which depicts the whole number of atoms of each element present in the compound.
In both the formulas, the nature of atoms remains the same but the number differs.
For Example: The molecular formula of oxalic acid is
but the empirical formula of oxalic acid is 
To calculate the molecular formula, we need to find the valency which is multiplied by each element to get the molecular formula.
The equation used to calculate the valency is:

The empirical mass can be calculated from empirical formula and molar mass must be known.
Explanation:
First, you have to know the definition of density. Density is mass per unit volume, or D = m/V. In this problem, you are given the mass = 37 g and you are given the volume of 21 cm3. So, the density is simply m/V = 37g/21cm3 = 1.76g/cm3. It's that simple.
Your answer would be A for your homework
In physics, net force<span> is the overall </span>force<span> acting on an object. In order to calculate the </span>net force<span>, the body is isolated and interactions with the environment or other constraints are represented as </span>forces<span> and torques in a free-body diagram.
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