Yes, @Al E. in the end there is just Cl2 missing. Can you please tell me where exactly happened the reduction? Which element reduced?
@Michael yeah, I've searched Ni3O4 on google and couldn't find much information. This exact redox was a task on my exam at university yesterday which got me all confused. I wasn't sure how to determine oxidation number in Ni3O4, in the test I wrote that two oxygen atoms in Ni3O4 are (-2) and other two are (-1), and Ni is (+2). Did balance it in the end, but I'm not very sure oxidation numbers are really like that. In a week or two I will get the results and ask professor what is the correct answer so I will let you know.