Which of the following BEST explains how matter and energy cycle through ecosystems?

When balancing a chemical equation:

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?

Which aqueous solution of ki freezes at the lowest temperature? 1) 1 mol of ki in 500. g of water 2) 2 mol of ki in 500. g of water 3) 1 mol of ki in 1000. g of water 4) 2 mol of ki in 1000. g of water