The symbol of helium is He and this distinguishes it from the symbol for hydrogen.
<h3>What are chemical symbols?</h3>
Chemical symbol are the means by which we designate elements on paper. The symbols could be one letter or two letter as the case may be. There is no chemical symbol that has more than two letters that are used to designate the element.
We know that hydrogen has the symbol H. There is to way that another element will also have the symbol H as that would be tantamount to confusion. As a result of that, the symbol of helium is He and this distinguishes it from the symbol for hydrogen.
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The answer is 40.
We can solve this by finding out the number of protons, and neutrons. Atomic number of an element means the number of protons in that element. So, the atom has 30 protons if the atomic number is 30.
On the other hand, mass number is the total number of protons and neutrons, but not electrons, because they're too light comparing to the other 2. Therefore, we can simply solve the number of neutrons in the atom by subtracting the number of protons from the mass number. 70 - 30 = 40.
Therfore, the number of neutrons is 40.
Answer: Option (b) is the correct answer.
Explanation:
A covalent compound is defined as the compound in which sharing of electrons take place between the combining atoms. Generally, when two or more non-metals chemically combine together the it will lead to the formation of a covalent compound.
For example, 
and HCl is also a covalent compound.
And, a compound in which transfer of electrons occur between the combining atoms is known as an ionic compound. Whenever, a metal chemically combines with a non-metal then it will always lead to the formation of an ionic compound.
For example, KI is an ionic compound.
Thus, we can conclude that and HCl are the two substances which are covalent compounds.
Explanation:
Since liquid isopropanol is a polar liquid and water is also a polar solvent. So, when both of them are added together then according to the like dissolves like principle they get dissolved.
At the molecular level, the polar molecules of isopropanol get attracted towards the polar molecules of water at the surface of water.
As a result, water molecules get surrounded by isopropanol. Thus, water molecules enter the solution and evenly spread into the solution.
