Can't say i can answer this. :/
Basically, the answer for this would be N or NITROGEN. If we combine nitrogen with chlorine, what happens is that, it can attract more chlorine electrons towards itself. The reason is that, nitrogen is considered more electronegative compared to chlorine. So best answer for this is the first option.
Personal experience from Ag Mech classes-Concrete cools faster than metal.
The number is is surely 1
