Net ionic equation for
HClO4(aq) + NaOH(aq) --> H2O (l) + NaClO4(aq).
for the molecular equation
HClO4 (aq) + NaOH(aq) --> H2O (l) + NaClO4 (aq)
the ionic equation is
H+ + ClO4- + Na+ + OH- --> H2O(l) + Na+ + ClO4-
now remove the spectator ions (Na+ and ClO4-) to give the net ionic equation
H+ + OH- --> H2O(l)