You are right, it's CA Calcium, 40.08, Group 2 and Row 4.
2HCO3 - + Ca2+ CaCO3 + CO2 + H2O Bicarbonate (HCO3-) combines with calcium ions in the water to make calcium carbonate (CaCO3, limestone). This process can occur both within organisms such as corals or as a simple chemical reaction in the water itself.
First choice: PhH4 has a lower boiling point
Second: SiF4 higher
Third: CBr4 higher
Because water vapor, uncontained, will diffuse out into the atmosphere and is not close enough to condense back into the liquid water, so no equilib. can be established.
