Explanation
The type of data replication that is required for a hot-site disaster recovery model is constant. A hot site is a type of disaster recovery site that has fully operational IT infrastructure and equipment that can take over the primary site's functions immediately in case of a disaster or disruption. A hot site requires constant data replication between the primary site and the hot site to ensure that the data is up-to-date and consistent.
Constant data replication means that any changes made to the data at the primary site are immediately copied to the hot site without any delay or lag.

An emergency change request is a type of change management activity that is used to address urgent issues that pose a significant risk to the organization, such as a system breach. An emergency change request requires immediate action and approval, and it may bypass some of the normal change management procedures, such as testing, documentation, or stakeholder communication12.
References = 1: Change Management Plans: A Definitive Guide -
Indeed(https://www.indeed.com/career-advice/career-development/change-management-activities) 2: The 10 Best Change Management Activities - Connecteam(https://connecteam.com/top-10-change-management-activities/)

A subnet mask is a number that distinguishes the network address and the host address within an IP address1. A subnet mask allows network traffic to understand IP addresses by splitting them into the network and host addresses. If the subnet mask is incorrect, the network traffic may not be able to determine the correct destination for the packets, and only reach some of the servers that have similar IP addresses. For example, if the new virtual server has an IP address of 192.168.1.100 and a subnet mask of 255.255.0.0, it can only communicate with servers that have IP addresses in the range of 192.168.0.0 to 192.168.255.2552. To fix this issue, the systems administrator needs to check and correct the subnet mask of the new virtual server according to the network configuration.