Correct Answer: is less dense when it is frozen. Response Feedback: Water expands as it freezes. Due to the hydrogen bonding of water molecules when water freezes, air is trapped between molecules. This will cause the water to occupy more space when frozen. The gap in the sidewalks helps to accommodate for this expansion. Question 16 1 out of 1 points Which one of the following is the smallest unit of matter that has all the properties of an element? Answer Selected Answer: atom
Correct Answer: atom Response Feedback: Elements are comprised of one kind of atom. These atoms all bear the same atomic number having a characteristic number or sub atomic particles that govern the properties of that element. Molecules have more than one atom present, so they are not in their simplest form. Compounds are comprised of two or more different elements. Question 17 1 out of 1 points In what ways are radioactive isotopes potentially harmful? Answer Selected Answer: Unmonitored release into the environment can make changes in a cell's DNA. Correct Answer: Unmonitored release into the environment can make changes in a cell's DNA. Response Feedback: Radioactive isotopes are important in biology and medicine. They can be used to trace molecular changes, destroy abnormal cells, and play a significant role in the ability to determine the age of biological specimens. Their danger comes in their unmonitored release into the environment where they can make changes in cells, damage DNA, cause cancer, or at their worst be lethal. Question 18 1 out of 1 points The reactivity of an atom depends on Answer Selected Answer: the number of valence electrons. Correct Answer: the number of valence electrons. Response Feedback: The bonds between different atoms arise from the giving, taking or sharing of the electrons in the outer energy level (valence electrons).
Question 19 1 out of 1 points Why do cells need buffering agents? Answer Selected Answer: to minimize the changes in pH of their internal environment Correct Answer: to minimize the changes in pH of their internal environment Response Feedback: Living organisms need to be kept within narrow pH ranges in order to maintain homeostasis. A buffer is able to keep pH within their normal limits by taking up excess hydrogen ions (H + ) or hydroxide ions (OH - ) in solution. Question 20 1 out of 1 points The particles that are found in the nucleus of an atom are the Answer Selected Answer: neutrons and protons. Correct Answer: neutrons and protons. Response Feedback: An atom is comprised of subatomic particles. The protons bear a positive charge, are found in the nucleus, and their number creates the atomic number assigned to that element. The neutrons are found in the nucleus as well and they with the protons create the majority of an atom's mass. The electrons bear a negative charge and govern the elements reactivity.