ARP

ARP request is Layer 2 broadcast. Since it knows the IP but needs the MAC of the host who is having that IP so its L2 Broadcast

Where as the ARP response is unicast. since the reciver knows the sender

But this not the scenario always, sometimes the ARP request might be unicast as well.. Image a scenario where the Host A resolves the MAC using the ARP request broadcast and response unicast. After the time out or before the timeout going to occur the Host A sends the ARP unicast request to check whether the Host B is still there or not. So it uses ARP unicast request. But still the Target Mac address in the ARP payload is 00:00:00:00:00:00

Proxy ARP, Gratuitous ARP

ARP video

Ipv6 doesn't uses ARP. It uses neighbor discovery

ARP Request

ARP Reply