What does 2 mean on MgBr2

What are the variables in gay-lussac’s law? pressure and volume pressure, temperature, and volume pressure and temperature volume, temperature, and moles of gas

Fill in the coefficients that will balance the following reaction: a0cr2(so4)3 + a1agno3

Which ocean zone has the most abundant primary producer and why a) the abyssopelagic zone ,du to the absence of light and cold water temperatureb) the bathypelagic zone, due to the absence of light and cold water temperaturec) the mesopelagic zone ,due to uts high light availability and warm water temperature d) the epipelagic zone,due to its high light availability and warm water temperature