Answer:
Percent composition tells you which types of atoms (elements) are present in a molecule and their levels. Percent composition can also tell you about the different elements present in an ionic compound as well.
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Answer: There are 
atoms of hydrogen are present in 40g of urea, 
.
Explanation:
Given: Mass of urea = 40 g
Number of moles is the mass of substance divided by its molar mass.
First, moles of urea (molar mass = 60 g/mol) are calculated as follows.
According to the mole concept, 1 mole of every substance contains 
atoms.
So, the number of atoms present in 0.67 moles are as follows.
In a molecule of urea there are 4 hydrogen atoms. Hence, number of hydrogen atoms present in 40 g of urea is as follows.
Thus, we can conclude that there are atoms of hydrogen are present in 40g of urea, .
Molecules may be similar or different on the basis of size, shape, structure and chemical composition.
<h2>Similarities and differences</h2>
Two molecules can be considered similar or different on the basis of size, shape, structure and chemical composition. The molecules in the two proposed systems are consider the same when they are similar in size, shapes, structure and chemical composition.
While on the other hand, the molecules is considered different when they have different structure and chemical composition so we can say that molecules may be similar or different on the basis of size, shape, structure and chemical composition.
Learn more about molecules here: brainly.com/question/26044300
Learn more: brainly.com/question/26268787
