n（H2SO4）=4.9g/98g/mol=0.05mol
n（O）=0.05mol*4=0.2mol
4.9克硫酸中含硫酸分子___mol，含氧原子___个
n（H2SO4）=4.9g/98g/mol=0.05mol
n（O）=0.05mol*4=0.2mol
n（H2SO4）=4.9g/98g/mol=0.05mol
n（O）=0.05mol*4=0.2mol
n（H2SO4）=4.9g/98g/mol=0.05mol
n（O）=0.05mol*4=0.2mol
n（H2SO4）=4.9g/98g/mol=0.05mol
n（O）=0.05mol*4=0.2mol