Which of the following is an oxidation-reduction reaction?
• so2(g) + h2o(1) h2so3(aq)
• caco3(s) , cao(s) + co2(g)
ca(oh)2(s) + h2co3(1) caco3(aq) + 2h2o(1)
• csh1206(s) + 602(9) _ , 6c02(g) + 6h20 (7

Iknow the answer is a but i don't know why

Consider hydrogen in an excited state n = 5n=5 that emits photons to reach the ground state. there are various possible transitions other than straight to the ground state that can occur; for example, it can drop to the n = 3n=3 state followed by the n = 3n=3 to the ground state transition. which of the possible transitions will result in the emission of a photon in the visible region?

Which symbol can be used to indicate the pressure at which a chemical reaction is carried out? 25°c 2 atm pa