Answer:
II and IV.
Explanation:
I. (INCORRECT). A model is a tentative to determinate a thing that can't be proved, and it's made based on evidence. If the model can explain the observation in nature, it is considered right, although it can be proved by a theory.
II. (CORRECT). The most accepted model of atoms says that they're formed by tiny particles, protons, neutrons, and electrons, with the first two on the nucleus, and the other surrounding it in an open space.
III. (INCORRECT). A heterogeneous mixture is a mixture of substances that is possible to identify phases of them, such as in oil and water. In the air, isn't possible to identify the constituents, and it's a homogeneous mixture.
IV. (CORRECT). Silver has atomic number 47, which is its number of protons. The atomic mass is the sum of protons and neutrons, so the number of neutrons is 108 - 47 = 61.
Answer: For every one mole of Ca used in this reaction, two mols of H20 are used, one mole of Ca(OH)2 is formed, and one mole of H2 is formed.
Explanation: Once the equation is balanced, you can get the ratio from the coefficients. If you are looking at the ratio of Ca to H2O, the ratio is 1:2; Ca to H2 1:1.
IAL is the suffix pertaining to conditions percent are birth.
Any chemical reaction would always result to a chemical change. If you can see observations of a change in color, bubbling or any liberation of gas, formation of a precipitate, or a change in temperature, then a chemical change has occurred. I can't say which combinations would result to a chemical change because there are no choices. I can only give an example. If HCl reacts with NaOH,
HCl + NaOH → NaCl + H₂O
This is a chemical change because a precipitate in the form of NaCl salt is formed.