Which of the following statements about water are true 1) water cover 75% of Earth 2) once water is used it can never be reused 3) only 3% of Earth’s water is fresh 4) water comprises the majority of all plants and animals.

Which one of the following is an oxidation-reduction reaction? naoh + hno3 --> h2o + kno3 naoh + hno3 --> h2o + kno3 so3 + h2o --> h2so4 cacl2 + na2co3 --> caco3 + 2 nacl ch4 + 2 o2 --> co2 + 2 h2o al2(so4)3 + 6 koh --> 2 al(oh)3 + 3 k2so4