Hello Faisal.
The concept behind ARP being L2 or L2.5 is a rather… contentious topic amongst many communities 
There are several arguments for and against.
For example, you already know what the IP address of your destination is. You then use ARP to learn the MAC address associated with that host/next hop for mapping purposes which is all L2.
But then again, you use layer 2 to provide layer 3 info. You can use it to confirm layer 3 configuration/information.
Oh but wait, ARP doesn’t actually use an IP header. Here is how it looks like in Wireshark
But then again, you can argue that ARP is the go-between IP and Ethernet and that it exists between these two protocols.
It’s a rather complicated topic to discuss and I don’t think that there is a clear definitive answer to this problem. My take on it is that it’s a layer 2 protocol. There is no IP Header and you already know the IP address, you just need the MAC address. As you’ve seen from the Wireshark capture, ARP lies on L2.
Whichever angle you take on it, there will be people who will agree and people who will disagree, atleast that’s how I view it. I wouldn’t bother too much with differentiating between whether it’s actually L2 or maybe L2.5. As long as you understand the protocol and what it does, you’re good for the exam and for the real world.
And good question, by the way! It’s always fun to have such discussions. It shows that you’re thinking about the protocol and not just accepting whatever your study resource mentions.
David