Nesesito ayuda no Le Entendi

Which of these reactions are redox reactions? check all that apply.cd + hcl → cdcl2  + h2cucl2  + na2s → 2nacl + cuscaco3  → cao + co2          2zns + 3o2  → 2zno + 2so2          ch4  + 2o2  → co2  + 2h2o

Use examples from the article to explain one positive and one negative effect that chemistry has had on society.

As changes in energy levels of electrons increase, the frequencies of atomic line spectra they emit