Question

seleniums oxidation number is -2. to become stable it must...
select one:
a. lose 2 electrons.
b. gain 2 electrons.
c. lose 4 electrons.
d. share 2 electrons.

which of the following is the correct formula for the compound formed by sulfur (oxidation number of -2) and sodium (oxidation number of +1)?
select one:
a. nas
b. na₃s₆
c. nas₂
d. na₂s

Explanation:

Step1: Analyze selenium's electron state

Selenium (oxidation number -2) has 2 extra electrons. To reach a stable noble gas electron configuration (8 valence electrons), it needs to lose these excess electrons.

Step2: Balance charges for sodium-sulfur compound

Sodium has oxidation number +1, sulfur has -2. Let the formula be $\text{Na}_x\text{S}_y$. We need $x(+1) + y(-2) = 0$. Solving for $x$ and $y$, $x=2$, $y=1$, so formula is $\text{Na}_2\text{S}$.

Answer:

1. a. lose 2 electrons
2. d. $\text{Na}_2\text{S}$