How many valence electrons does manganese have?

7 valence electrons

This means that manganese (Mn group-7) has the electron configuration [Ar]4s²3d⁵ and 7 valence electrons, this can have valence from +1–7 ,but generally manganese in its compounds has valency of +2,+4,+7 due to corresponding stable electronic configuration.

a. the law of proportion states the combination of 2 atoms in a specific ratio to produce multiple compounds such as the given statement of question ‘1st compound contains 88.8 % cu ’ indicates 88.8 g of cu is present along with 11.2 g oxygen in 100 g of compound whereas the statement ‘2st compound contains 79.9 % cu ’ indicates 79.9 g of cu is present along with 20.1 g oxygen in 100 g of compound

1st compound contains 88.8 g cu

for cu

m = 63 g /mol

atomic % = 88.8 /63 = 1.42

for o

m = 16 g /mol

atomic % = 11.2 /16 = 0.7

b. the emperical formula of 1st compound is

cu1.4o0.7

cu2o