The gas phase decomposition of phosphine at 120 °c ph3(g) 1/4 p4(g) + 3/2 h2(g) is first order in ph3 with a rate constant of 1.80×10-2 s-1. if the initial concentration of ph3 is 3.16×10-2 m, the concentration of ph3 will be m after 99 s have passed

I'm learning about the periodic tables and what each subject's configuration is. for example, hydrogen is 1s^1, but i don't understand how you get that. can someone me understand how to figure out how to figure this out? sorry if the question makes no sense, but it would really a lot if you could me understand! you so much if you can!