Explanation

QoS concept: Class of Service Definition: 3) A method for classifying network traffic using access categories based on the IEEE 802.11e QoS standards QoS concept: Differentiated services Definition: 2) A method for classifying network traffic at layer-3 or marking packets with one of 64 different service classes QoS concept: WMM Definition: 4) A method for classifying network traffic using access categories based on the IEEE 802.11e QoS standards

According to the Aruba Documentation Portal1, PAPI (Port Aggregation Protocol) is a protocol that allows multiple physical ports to be aggregated into a single logical port for increased bandwidth and performance. PAPI can be used between AOS-CX switches and gateways, or between AOS-CX switches and other devices.
Option A: Implement an IPSec tunnel to protect PAPI between the AOS-CX switches and the gateway This is because option A shows how to implement an IPSec tunnel between two devices using the interface command and the ipsec command. An IPSec tunnel can provide encryption and authentication for PAPI traffic between two devices, such as an AOS-CX switch and a gateway2.
Therefore, option A is a feasible option to protect this traffic.
I hope this helps you. If you need more information, please let me know.
1: https://www.arubanetworks.com/techdocs/AOS-CX/10.06/HTML/5200-7727/Content/Chp_prev_traf_loss/Act_gtw_act_fwd/act-gat-ove-vsx-10.htm 2: https://community.arubanetworks.com/blogviewer?blogkey=989fc43a-e0df-42db-9c0b-f96d6565a1fa

Explanation
The command loop-protect enables loop protection on each layer 2 interface (port, LAG, or VLAN) for which loop protection is needed. Loop protection can find loops in untagged layer 2 links, as well as on tagged VLANs.

Explanation
To allow a new VLAN 100 between VSX pair inter-switch-link 256 for port 1/45 and 2/45, you need to use the command vlan trunk allowed 100 in LAG256. This will add VLAN 100 to the list of allowed VLANs on the trunk port LAG256, which is part of the inter-switch-link between VSX peers. The other options are incorrect because they either do not use the correct command or do not specify the correct port or VLAN.
References: https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-ch07.html
https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-ch02.html

Active Gateway is the first-hop protocol feature that is used for VSX L3 gateway as per Aruba recommendation. Active Gateway is a feature that allows both VSX peers to act as active gateways for different subnets, eliminating the need for VRRP or other first-hop redundancy protocols. Active Gateway also provides fast failover and load balancing for L3 traffic across the VSX peers. The other options are incorrect because they are either not recommended or not supported by Aruba CX VSX. Reference: https://www.arubanetworks.com/techdocs/AOS-CX/10.04/HTML/5200-6728/bk01-ch07.html https://www.arubanetworks.com/resource/aruba-virtual-switching-extension-vsx/