What type of mount allows the optic to be placed on the service rifle?

The correct choice is the TA51 mount, which is designed specifically to accommodate optics on service rifles, such as the M4 or similar platforms. This mount provides a secure and stable platform for various optical sights, allowing for improved target acquisition and accuracy.

The TA51 mount is particularly notable for its durability and compatibility with various types of optics, ensuring that the sight remains securely attached during use. It is also designed with military standards in mind, reflecting the rugged conditions that service rifles may encounter in the field.

In the context of the other options, while they may exist as mounts or components for different applications, they do not specifically focus on the service rifles in the same way that the TA51 does, making it the most appropriate choice for optics mounting on those weapons.