Is a snake a first second or third level consumer?

The short answer is, "NO". they are considered 2nd level consumers.

First level consumers are animals such as Mice, who feed on plants, plant-based, etc..

Since a Rattlesnake would eat a mouse, it would be considered 2nd level.

An example of a 3rd level consumer would be a hawk, or some other bird of prey, eating the snake.