Thermal expansion happens when

The coefficient of thermal expansion describes how the size of an object changes with a change in temperature. ... In general, substances expand or contract when their temperature changes, with expansion or contraction occurring in all directions.

the size of an object changes with a change in temperature.

Explanation:

the term hydride is commonly named after binary compounds that hydrogen forms with other elements of the periodic table. hydride compounds in general form with almost any element, except a few noble gases. the trends and properties vary according to the type of intermolecular force that bonds the elements together, the temperature, its molecular masses, and other components. hydrides are classified into three major groups, depending on what elements the hydrogen bonds to. the three major groups are covalent, ionic, and metallic hydrides. formally, hydride is known as the negative ion of a hydrogen, h-, also called a hydride ion. because of this negative charge, hydrides have reducing, or basic properties. its special characteristics will be further discussed.

explanation:

∠gdh and ∠edh on edg.

answer is c