21. A chemist mixed two substances together: a blue powder with no smell and a colorless liquid with a strong smell. Their repeating groups of atoms
are shown above on the left. After they were mixed, the chemist analyzed
the results and found two substances. One ending substance had the
repeating group of atoms shown above on the right. Is the ending
substance the same substance as the blue powder? What happened to
the atoms of the starting substances when the ending substances
formed?

the population of unionid mussels in the hudson river decreased after zebra mussels were introduced. zebra mussels, a nonnative species, competed with the unionid mussels for food. the zebra mussels were able to outcompete the unionid mussels, allowing the zebra mussel population to increase dramatically over six years. the unionid mussel population decreased due to a lack of food.

hope this :

a chemical change results in a new substance being formed; whereas a physical change will result in a different state of matter

explanation: