Finding oxidation numbers of Mn in five compounds

[yuuri14]

determine the oxidation number for Mn in each of the following:
a) KMnO4
is the ox # -3

b) LiMnO2
is the ox # +1
c) MnO2
is the ox # +2
d)K2 MnCl
is the ox # +1
e)Mn2 O7
is the ox # -10

I need help ASAP PLEASE!

 

[Fightfish]

Do you know how to compute oxidation numbers in the first place? All of them are wrong. Also, oxidation numbers must have a +/- sign.

 

[daviddee305]

to determine the oxidation numbers you need to rewrite the compound using the charge of the atoms. For (a), the charge of K is +1, because K is in an Alkali metal and all Alkali metals are plus 1. The charge of O is -2 -- and you have 4 oxygens. The compound KMnO₄ has no charge. So...

KMnO₄ = (+1) + Mn + (-2)(4) = 0

Do the algebra and Mn = +7