Qodriyah, L., Mulyastuti, H. and Hadi, W.P. 2026. Development of Problem-Solving Skills Instrument in the Context of Toroan Waterfall: A Validity Study. Equator Science Journal. 4, 3 (Oct. 2026), 425–436. DOI:https://doi.org/10.61142/esj.v4i3.496.