What's the most abundant elements

Hydrogen and Oxygen.

Explanation:

The most abundant element in the universe is the Hydrogen which 75% of the universe and remaining 25% is covered by the Helium. The Oxygen is the third most abundant element of the Universe as its mainly found only on the planet earth and the scientists are still finding oxygen in the outer earth.

On the Earth, the most abundant element in the crust is Oxygen which covers 46.6% of the total elements in the crust and the element abundant after oxygen in the earth crust is the Silicon with 27.7%

For Human body, the most abundant element is the Oxygen which Includes 65% of the total body weight.

So, the Hydrogen and Oxygen are the two most abundant element of the Universe also vital elements of the human body.