Strontium is a metal that is responsible for producing the beautiful RED COLOR in a Fireworks display. It has 3 different isotopes. Strontium-86 is 10.2% abundant. Strontium-87 is 7.3% abundant and Strontium-88 is 82.5% abundant. Calculate the Average Atomic Mass for Strontium. All work must be shown to receive Maximum Credit * 5 points

Iknow the answer is a but i don't know why

Consider a culture medium on which only gram-positive organisms such as staphylococcus aureus colonies can grow due to an elevated nacl level. a yellow halo surrounds the growth, indicating the bacterium fermented a sugar in the medium, decreasing the ph as a result and changing the color of a ph indicator chemical. this type of medium would be referred to as a differential and enrichment culture.

The kw for water at 0 °c is 0.12× 10–14 m2. calculate the ph of a neutral aqueous solution at 0 °c.