Question

as the sun ages, we will see the amount of hydrogen ------ and the amount of helium ------.

Explanation:

Step1: Recall Stellar Evolution Basics

In the Sun (a main - sequence star), nuclear fusion occurs in the core, where hydrogen ($\ce{H}$) is fused into helium ($\ce{He}$). As the Sun ages, it will consume more of its hydrogen fuel for fusion.

Step2: Analyze Hydrogen Amount

Since hydrogen is being used up in the fusion process to form helium, the amount of hydrogen in the Sun will decrease over time.

Step3: Analyze Helium Amount

As hydrogen is fused into helium, the product of this fusion (helium) will accumulate in the core. So, the amount of helium in the Sun will increase as the Sun ages.

Answer:

Decrease; Increase