At 25 °C the solubility product constants for three sparingly soluble salts are:
• Ag₂CO₃ : 8.1×10−12
• PbBr₂ : 6.6×10−6
• SrF₂ : 7.9×10−10
Rank these compounds in order of increasing molar solubility in pure water at 25 °C. Write only the formulas, separated by “<”.