Explain why photocells contain gold nanoparticles rather than a solid piece of gold please help me it would be much appreciated, ill give the brainiest

One similarity and one difference between an element and a mixture of elements

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.

If this sedimentary rock layer is truly the oldest one of marine origin, what do you think that tells usabout the formation of earth's oceans?