An atom’s emission of light with a specific amount of energy confirms that atoms must have a dense central mass surrounded by electrons at a distance. electrons emit and absorb energy based on their position around the nucleus. electrons can only be found within predicted areas surrounding the nucleus. atoms are made of positive and negative charges.

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.