Question

question 39
isotopes of an element have

a the same atomic number and same atomic weight.

b the same atomic number but different atomic weights.

c different atomic numbers but the same atomic weight.

d different atomic numbers and different atomic weights.

question 40

nucleic acids are

a very small, simple molecules.

b structural molecules that have no function other than support.

c composed of building blocks called nucleotides.

d primary sources of cellular energy.

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Explanation:

Question 39

Isotopes are atoms of the same element with the same atomic number (number of protons) but different numbers of neutrons, which leads to different atomic weights (mass number = protons + neutrons). So option B is correct.

Nucleic acids (DNA and RNA) are composed of nucleotides as their building blocks. Option A is wrong as they are complex; option B is wrong as they have genetic functions; option D is wrong as carbohydrates are primary energy sources. So option C is correct.

Answer:

B. the same atomic number but different atomic weights.

Question 40