Now that you have examined the changes in co2 concentration within each year, consider the changes that occurred between the years 1990 and 2010. begin by calculating the average co2 concentration for the 12 months of each year. what was the average co2 concentration in 1990?

354.5 ppm is the Answer. 

The density of water is 1 g/cm cubed and in order for the pebble to sink its density has to be greater than the density of water and in order for the twig to float its density has to be less than the density of water

Answerit curves up and levels out.explanationwe assume that the container contains absolutely no ammonia to begin with as it states that "nitrogen gas and hydrogen gas" react to "produce ammonia."at dynamic equilibrium, the product and reactant concentrations are equal.this means that, starting from a concentration of zero, [nh₃] must curve "up" from zero and then level out to a constant concentration.