Which equation obeys the law of conservation of mass? H2(g) + O2(g) → H2O(g) H2(g) + O2(g) → H2O(g) +4He(g) 2H2(g) + O2(g) → 2H2O(g) H2(g) → H2O(g) H2(g) + O2(g) → 2H2O(g)

The chemical composition of soil varies with depth. an article in communications in soil science and plant analysis describes chemical analyses of soil taken from a farm in western australia. fifty specimens were each taken at depths 50 and 250 cm. at a depth of 50 cm, the average no3 concentration (in mg/l) was 88.5 with a standard deviation of 49.4. at a depth of 250 cm, the average concentration was 110.6 with a standard deviation of 51.5. find a 95% confidence interval for the difference in no3 concentrations at the two depths.