Question

?Cr2(SO4)3 + ?NaOH= ?[Cr(OH)2]2SO4+? 
?FeOHSO4 + KOH=?[Fe(OH)2]SO4+? 
?[Fe(OH)2]2SO4 +?H2SO4=?(FeOH)SO4 +?H2O

Answer 1

$Cr_2(SO_4)_3+6NaOH=3Na_2SO_4+2Cr(OH)_3$(осадок)
$2 FeOHSO_4 + 2 KOH = [Fe(OH)_2]_2SO_4 + K_2SO_4$
$[Fe(OH)_2]_2SO_4 + H_2SO_4 = 2 (FeOH)SO_4 + 2 H_2O$