Final answer:
A watch glass is ideally suited to cover a beaker during a chemistry experiment to prevent spattering while still allowing gases to escape.
Step-by-step explanation:
To cover a beaker during a reaction between nitric acid and tin metal to prevent spattering, a watch glass is typically used. A watch glass is a circular, slightly concave piece of glass that fits on top of a beaker. It allows gases to escape while preventing any splashing out of the beaker. In a laboratory setting, following appropriate safety procedures is critical, including the use of the correct equipment to ensure that reactions are contained and personnel are protected.