In ARP request, the destination MAC is broadcasted (all 1's) and the packet is sent to the local subnet.
Do not confuse yourself that MAC is required then why IP is not broadcast? See it this way: If destination IP is broadcast, how would the destination machine ever know that its MAC has been requested by someone.
To clear confusion, you've 4 fields
SIP • DestIP • SMAC • DESTMAC
Try filling these fields, if you broadcast ip (all 1's in DestIP), and you want to know the destination MAC, is there any way the destination machine can recognise that its MAC has been requested by a machine with SIP and SMAC address?
The correct answer was broadcast MAC in local subnet.