Element that has mass number of 20

Needthe meter is the standard unit for: 1) height 2) length 3) weight 4) mass

You are making a solution of calcium chloride dissolved in water. you add solid, stir, and it dissolves. you add just a spatula tip full, stir, and the solid does not dissolve. how could you describe the solutions before and after adding the spatula tip amount

In the space, show a correct numerical setup for calculating the number of moles of co2 present in 11 grams of co2