Gamma rays<span> are </span>produced<span> in the disintegration of radioactive atomic nuclei and in the decay of certain subatomic particles. When an unstable atomic nucleus decays into a more stable nucleus, the “daughter” nucleus is sometimes </span>produced<span> in an excited state.</span>
He produced the first orderly arrangement of known elements, he used patterns to predict undiscovered elements

As per as my knowledge
The speed of a wave in a medium is affected by <u>d</u><u>e</u><u>n</u><u>s</u><u>i</u><u>t</u><u>y</u>,<u> </u><u>w</u><u>a</u><u>v</u><u>e</u><u>l</u><u>e</u><u>n</u><u>g</u><u>t</u><u>h</u> and <u>t</u><u>e</u><u>m</u><u>p</u><u>e</u><u>r</u><u>a</u><u>t</u><u>u</u><u>r</u><u>e</u><u> </u>:)
(Good luck on your test and mark me brainliest if this helps)