Sorting(decreasing ord) a dataframe.groupby according to a column value

Question

I have a dataframe as below:

col1=[1,1,1,2,2,2,3,3,3]
col2=[\'a\',\'b\',\'c\',\'d\',\'e\',\'f\',\'g\',\'h\',\'i\']
col3=[1,2,3,2,3,1,3,1,2]
d={
    "col1