rhs specifies that tests for heteroskedasticity be performed for the right-hand-side  (explanatory) variables of the fitted regression model.  The rhs option may be combined with a varlist.

normal, the default, causes estat hettest to compute the original Breusch-Pagan/Cook-Weisberg test, which assumes that the regression disturbances are normally distributed.
iid causes estat hettest to compute the N*R2 version of the score test that drops thenormality assumption.


fstat causes estat hettest to compute the F-statistic version that drops the normality assumption.


mtest[(spec)] specifies that multiple testing be performed.  The argument specifies how  p-values are adjusted.