Answer:
There is one single covalent bond between two carbon atoms.
Explanation:
We know that sharing of electrons form covalent bonds.
If we look upon K,L,M ,N shells of the carbon and hydrogen atoms.
We found that Hydrogen is having only
electron in K shell.
And Carbon on the other hand is having
electrons in K shell and
electrons in L shell.
So carbon have
valence electrons,and it can share
bonds with any relevant atom to complete its octet.
And Hydrogen requires
electron to complete its doublet.
Alkane general formula 
For ethane 

Carbon atom is shared by
Hydrogen.
The remaining one electron
of carbon will be shared with another carbon atom.
An image of the sharing of electrons attached below,
Hence we have only
covalent bond between the two.
NaCl is salt to it is obviously SOLUBLE :)
I think it is rarefaction. But im not sure
<span>polyethylene or polythene are the main ingredients </span>
Answer is: <span>it comes at the right time.
Some of the chemistry discoveries that come in right time (with enough informations, knowledge and right technology to use that discovery) are: </span>Periodic Table of the Elements, discovery of electron, proton, neutron, radioactivity, pasteurization, t<span>he Haber-Bosch process.</span>