Which diagram above has 4 valence electrons?

Abike ride event is 30 miles. a first aid tent is put at the 3/4 mark of the course. how many miles from the starting point is the first aid tent?

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.

Use the periodic table to classify each of the elements below. cadmium (cd): vanadium (v): xenon (xe): iodine (i): potassium (k): strontium (sr):