The measure of the amount of matter is known as ?

This is a characteristic of the elements in the periodic table that shows a pattern. it may increase or decrease across or down the table.

Before it was launched, a helium-filled balloon had a pressure of 201 kpa at a temperature of 27°c. at an altitude of 15,000 m, the pressure had decreased to 2.5 kpa and the temperature had dropped to -14 °c. the volume of the balloon increased to 59.3 m3. what is the original volume of the balloon? 13 m3 0.85 m3 0.077 m3 1.17 m3

When did stem cell research become known ? who discovered stem cell? what experiments or studies have been conducted so far?