Note down the formula below
[tex]\boxed{\sf Mass\%\;of\; element=\dfrac{Mass\:of\:the\: element}{Mass\;of\:the\: compound}\times 100}[/tex]
Mass of the compound
[tex]\\ \sf\longmapsto 15+120=135g[/tex]
Mass % of Hydrogen:-
[tex]\\ \sf\longmapsto \dfrac{15}{135}\times 100[/tex]
[tex]\\ \sf\longmapsto \dfrac{1}{9}\times 100[/tex]
[tex]\\ \sf\longmapsto 11.1\%[/tex]
Mass % of Oxygen:-
[tex]\\ \sf\longmapsto \dfrac{120}{135}\times 100[/tex]
[tex]\\ \sf\longmapsto \dfrac{8}{9}\times 100[/tex]
[tex]\\ \sf\longmapsto 88.9\%[/tex]
