7. Which of the following statements about a spring balance and/or a chemical balance is/are correct? I. The chemical balance operates on the principle of moments. II. The spring balance operates on Hooke's law. III. Either may be used to measure the weight of a substance. IV. The reading of a spring balance never changes over the surface of the earth, while that of the chemical balance remains constant.
I and III
I and II
II and III
All of the ahove
AA
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