Weather dhcp offer is unicast or not?

The answer is yes. The RFC 1541 states that a server "should" try unicast first, but then can use broadcast when offering. Some OS's like Microsoft skip the unicast part of this as it is not required.

I would like to improve upon this answer

As i see in RFC 1541, server would try to unicast DHCP offer in case it has received DHCP Discover from a DHCP relay agent otherwise it would broadcast.

Would like to know if anybody differ in opinion....