C. The mass number is the amount of Protons and electrons there are combined, so 200 - 80 is 120.
Answer:
Solutions are always homogeneous.
Explanation:
Solution:
Solution are considered homogeneous because in solution the ratio of solute and solvent remain the same throughout the solution. Both solute and solvent are chemically combined and form a new substance.
In solution the particles of solute can not be seen through naked eye.
When the light is passed through the solution it can not scattered.
Example:
When salt is dissolve in water it makes a solution.
The solution also exist in gaseous form. For example oxygen and many other gases dissolved in nitrogen also form a solution.
Mixture:
In mixture substance are physically combined. In mixture every every individual particle retain their properties.
It can be consist of solid, liquid and gas.
Examples:
Sand in water is also a mixture.
Oil in water form mixture.
The pebbles become smooth and even because of erosion. the waves from the sea rub against the pebbles this is erosion. x
Answer:
C. 
Explanation:
Molecules with the stronger intermolecular forces are pulled tightly together to form solid at higher temperatures and that's why the freezing point is higher.
Also, molecules with the stronger intermolecular force have greater interaction between the molecules and thus on heating do not boil easily and have high boiling point also.
Thus, melting point and boiling point increases with increase in number of carbon atoms and also increase in intermolecular forces (like hydrogen bonding, if present).
Thus, the compound which is gas at room temperature is
<u>because it has least number of carbon atoms and absence of hydrogen bonding.</u>
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