Statement (I) is true: The active phosphorus-bearing compound in single superphosphate (SSP, $16\%\ \text{P}_2\text{O}_5$), double superphosphate (DSP, $32\%\ \text{P}_2\text{O}_5$), and triple superphosphate (TSP, $46 - 48\%\ \text{P}_2\text{O}_5$) is monocalcium phosphate monohydrate [$\text{Ca}(\text{H}_2\text{PO}_4)_2\cdot \text{H}_2\text{O}$].
Statement (II) is false: Although monocalcium phosphate is water-soluble, when applied to soils it reacts almost instantaneously with soil components (a process known as phosphate fixation/precipitation/adsorption with $\text{Ca}^{2+}$ in alkaline soils and with $\text{Fe}^{3+}/\text{Al}^{3+}$ in acidic soils). Because phosphate is rapidly converted into insoluble forms, leaching losses of phosphorus in agricultural soils are virtually negligible (typically $\lt 1\%$) under normal conditions.