use strict;
use warnings;

my %Hash = (
    a => [ qw( i ii iii ) ],
    b => [ qw( iv v vi ) ],
);

# one way to do it
for my $var ( sort keys %Hash ) {
    my $array_ref = $Hash{$var};
    for my $element ( @{$array_ref} ) {
        print "$element,";
    }
}

exit;