The measure of the tendency of an atom in a molecule to attract shared electrons is known as

• Copper ($\text{Cu}$): $1 \times 63.5 = 63.5$
• Sulfur ($\text{S}$): $1 \times 32.0 = 32.0$
• Oxygen ($\text{O}$ in $\text{SO}_4$): $4 \times 16.0 = 64.0$
• Water ($\text{H}_2\text{O}$): $2 \times 1.0 (\text{H}) + 1 \times 16.0 (\text{O}) = 2.0 + 16.0 = 18.0$

The compound contains one $\text{CuSO}_4$ unit and five $\text{H}_2\text{O}$ units.

The correct answer is A. 249.5 g.

25. All pure substances which are not elements are
Pure substances are classified into two categories: elements (which cannot be broken down further by chemical means) and compounds (which are formed when two or more elements are chemically combined in fixed proportions). Mixtures are not pure substances.
The correct answer is A. compounds.

26. A neutron striking an unstable nucleus may split it, causing the process known as
This process, where a heavy atomic nucleus splits into two or more smaller nuclei when struck by a neutron, is called nuclear fission. It releases a large amount of energy.
The correct answer is A. nuclear fission.

27. The valence electrons in magnesium are in the
Magnesium ($\text{Mg}$) has an atomic number of 12. Its electron configuration is $1s^2 2s^2 2p^6 3s^2$. The valence electrons are the electrons in the outermost principal energy level, which is the 3rd shell in this case. These are the two electrons in the 3s orbital.
The correct answer is D. 3s orbital.