SrBr₂ + (NH₄)₂CO₃ → SrCO₃ + 2NH₄Br what is the coeffieicent

Which best describes the present-day universe? opaque, expanding very slowly, stars produce heavy elements transparent, expanding at an accelerated rate, stars produce heavy elements opaque, expanding at an accelerated rate, stars produce only hydrogen and helium transparent, expanding very slowly, stars produce only hydrogen and helium

Areaction is first order. if the initial reactant concentration is 0.0200 m, and 25.0 days later the concentration is 6.25 x 10-4 m, then its half-life is:

A250 g sample of water with an initial temperatureof 98.8 closes 6500 joules of heat. what is the finaltemperature of the water?