Copy it I think hp[e that is right lol
Answer is: elements in group 1 will lose electrons to obtain a noble gas structure. They will lose 1 electron.
For example ₃Li 1s²2s¹ will lose one electron from 2s oribtal to obtain helium structure ₂He 1s².
Or sodium ₁₁Na 1s²2s²2p⁶3s¹ will also lose one electron to obtain neon structure ₁₀Ne 1s²2s²2p⁶.
The oxidation number of chlorine can be determined by identifying first the oxidation numbers of oxygen and Na. Oxygen has a charge of -2 and has a total of -8. Na has +1. To make the total zero, Cl has to have a charge of +7.
Probably life science or biology.