sari, novieta, et al. “The Difficulties of X Grade High School Students in Palangka Raya City Academic Year of 2018 2019 in Understanding Chemical Bond Concept Using Two-Tier Multiple Choice ”. GAMAPROIONUKLEUS, vol. 1, no. 2, Nov. 2020, pp. 135-48, doi:10.37304/jpmipa.v1i2.3686.