how many electrons should an atom already have in its outer shell if it wants to gain electrons an became an iron

How are the terms group and period used on the periodic table

The activation energy for the reaction no2(g)+co2(g)⟶no(g)+co(g) is ea = 300 kj/mol and the change in enthalpy for the reaction is δh = -100 kj/mol . what is the activation energy for the reverse reaction?

Which element forms a compound with chlorine with the general formula mci?