Answer:
Group 18th
Explanation:
The group 18th of periodic table which is composed of Noble gases mainly was missing from the Mendeleev's periodic table. The reason for this is that Noble gases are least reactive, therefore, it was difficult to predict such elements which do not react with other elements.
Answer: 4.5 moles of 
can be made from complete reaction of 3.0 moles of Al.
Explanation:
The given reaction equation is as follows.
This shows that 2 moles of Al reacts with 6 moles of HCl. So, the amount of HCl required to react with 1 mole Al is three times the amount of HCl.
Therefore, 3 moles of Al will react with 9 moles of HCl to give 3 moles of 
and 
moles of .
The reaction equation now will be as follows.
The moles can also be written as 4.5 moles.
Thus, we can conclude that 4.5 moles of can be made from complete reaction of 3.0 moles of Al.
Explanation:
The atomic number is equal to the number of protons in an atom's nucleus. Hydrogen's atomic number is 1 because all hydrogen atoms contain exactly one proton.
C:H:O = 40/12 : 6,7/1 : 53,3/16 = 3,33 : 6,7 : 3,33 ≈ 1 : 2 : 1
CH₂O
They are in order according to their atomic number, so the position should tell you the atomic number.
