Increased density decreases the speed of sound in a medium. While increased density can mean increased rigidity, or stiffness, it is not always the case. Greater density can be due to each molecule or atom having more momentum, and being slower to respond to the vibration of its neighbor.
Barium nitride
copy the name of the metal as it is written in the periodic table and the first part of the name of the nonmetal (nitrogen) and replace the end by "ide"
One of the two products of this reaction is carbonic acid (H2CO3), which immediately forms water and the gas you identified after exposure to the flaming and glowing splints. Write a balanced equation showing the decomposition of carbonic acid.