Why is the core considered the most dense layer of the earth?

Can you guys me with question no. 5!

If the concentration of phosphate in the cytosol is 2.0 mm and the concentration of phosphate in the surrounding fluid is 0.1 mm, how could the cell increase the concentration of phosphate in the cytosol? a) passive transportb) diffusionc) active transportd) osmosise) facilitated diffusion

In water, a strong acid will break down into its component parts. a. completely b. partly c. never in water, a weak base will break down into its component parts. a. completely b. partly c. never