A chemist added hydrochloric acid to a sample of baking soda in a beaker. Immediately, the mixture of the two chemicals began to fizz and bubble. Which of the following observations about the fizzing mixture provides evidence of a chemical reaction?

A. The temperature of the beaker did not change.

B. A substance escaped from the beaker in the form of a gas.

C. Some of the baking soda remained in the bottom of the beaker.

D. Most of the baking soda appeared to dissolve in the acid.

acid rain does not usually kill trees directly. instead, it is more likely to weaken the trees by damaging their leaves, limiting the nutrients available to them, or poisoning them with toxic substances slowly released from the soil. the main atmospheric pollutants that affect trees are nitrates and sulphates.

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.

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