$1)$$3C_2H_5OH+K_2Cr_2O_7+4H_2SO_4\rightarrow 3CH_3CHO+K_2SO_4+Cr_2(SO_4)_3+7H_2O$
$CH_3CHO+2AgNO_3+3NH_3+H_2O\rightarrow 2Ag\downarrow+2NH_4NO_3+CH_3COONH_4$
$Ag+2HNO_3\rightarrow AgNO_3+NO_2\uparrow+H_2O$
$n_{C_2H_5OH}=\frac{48}{46} mol\Rightarrow n_{NO_2 lt}=\frac{2.48}{46}$
$\Rightarrow H=\frac{25,76}{\frac{22,4.2.48}{46}}.100=55,1\%$