The superscript represents nuclear mass; here it is #1#, and thus there is ONE proton in the nucleus, one positively charged, massive particle. Around the nucleus, ONE electron is conceived to circulate, to orbit. And we assign a negative charge to this particle, and its mass is negligible.
The #1# subscript in #""_1^1H# is superfluous. The symbol #H# specifies an atomic number, #Z=1#.
Other isotopes of hydrogen exist, for instance #"deuterium"#, #""^2H#, which has (necessarily) one nuclear proton (why necessarily, given what I have said?) and what else, and also the #"tritium"# isotope, #""^3H#. How many neutrons here?
