What is the symbol for an ion with 16 pretons,18 neutrons an

What is the symbol for an ion with 16 pretons,18 neutrons and 18 electrons?
What is the symbol for an ion that has 16 pretons,16 neutrons and 18 electrons?
The sum of the number of neutrons and the number of electrons of 35 Cl- is________(35在上17在下）
17
A sample of methane( CH4) gas contains a samll amount of helium.Calculate the volume percentage of helium if the density of the sample is 0.709g/L at STP.
不是求翻译..