D except for the transition metals copper iron tantalum etc they have different oxidation states so arent fixed shells but all main group elements are grouped by the valence electrons sodium potassium lithium alkali column 1 valence electron highly reactive.
Answer:
A
Explanation:
We are usually asked to close the valve of the gas cylinder in our various kitchens at home <u>due to the inflammable property of the Liquified Petroleum Gas.</u>
<em>Without closing the valve, the LPG would diffuse into our homes, and any form of spark would cause an explosion and lead to a fire. Lives and properties could be lost in the process.</em>
The correct option is A.
Answer: number of atoms is 5.21 · 10^24
Explanation: Atomic mass of Be is 9.012 g/mol.
Number of moles n = m/M = 78.0 g / 9.012 g/mol =
Multiply this with Avogadro number Na = 6.022*10^23 1/mol
