systemd timer units are a type of systemd unit files that define when and how to activate another systemd unit, usually a service unit. Each timer unit has a corresponding service unit that it controls, and by default, the name of the timer unit matches the name of the service unit, except for the suffix. For example, a timer unit named foo.timer activates and manages a service unit named foo.service. The service unit defines what to run when the timer elapses, and the timer unit defines when and how to run the service unit. The timer unit can specify different types of timers, such as calendar-based or monotonic timers, and various options to control the frequency, accuracy, and persistence of the timer. The timer unit can also override the service unit to activate by using the Unit= option in the [Timer] section of the timer unit file.
The other statements listed are false regarding systemd timer units. Timer units are not defined within a service unit's file, but in a separate file with the .timer extension. The command executed by the timer is not specified in the timer unit's file, but in the service unit's file that the timer controls. There is no dedicated system service named systemd-cron that handles the execution of timer units, as timer units are managed by systemd itself. Timer units can exist in both the system scope and the user scope, and users can create and manage their own timer units in their home directories. References:
* systemd/Timers - ArchWiki
* systemd.timer - freedesktop.org
* Working with systemd Timers - SUSE Documentation

crontab

The traceroute program can be used to determine the routing path to a given destination by sending packets with incrementing TTL values and recording the source of the ICMP time exceeded messages. This way, it can show the intermediate hops and the round-trip times for each packet. The other programs have different purposes: dig is used to query DNS servers, netstat is used to display network connections and statistics, ping is used to test the reachability of a host by sending ICMP echo requests and measuring the response time, and route is used to manipulate the routing table. References:
* LPI 102-500 Exam Objectives, Topic 110: Network Fundamentals, Weight: 4, 110.3 Basic network troubleshooting
* LPI 102-500 Study Guide, Chapter 10: Network Fundamentals, Section 10.3: Basic Network Troubleshooting, Page 125-126

The command to delete the default gateway from the system IP routing table is either route del default or ip route del default. Both commands will remove the default route that matches the specified parameters.
The route command is the older and more widely supported tool, while the ip command is the newer and more powerful tool that can manipulate various aspects of the network configuration. The other options are either invalid or do not affect the default gateway. References:
* 1: How to Remove Default Gateways via ip | Baeldung on Linux
* 2: How to remove all default gateways - Unix & Linux Stack Exchange
* 4: How to Add or Change the Default Gateway in Linux: 9 Steps - wikiHow