About 98 percent of the mass of every living organism is composed of just six elements including carbon, hydrogen, nitrogen, oxygen and :

Explanation

The correct answer is Phosphorus and Calcium. In the context of biological molecules, the six elements that make up about 98% of the mass of living organisms are carbon (C), hydrogen (H), nitrogen (N), oxygen (O), phosphorus (P), and sulfur (S). Although phosphorus is included, calcium is more of a structural element in bones and is not one of the primary elements constituting the majority of living organism mass.Option A (Carbon and Sulfur) is incorrect because, while carbon is essential, sulfur is not one of the six key elements. Option C (Sulfur and Magnesium) is incorrect as magnesium is a trace element and not one of the primary six. Option D (Magnesium and Sodium) is also incorrect for similar reasons: both are trace elements and do not account for the bulk of the mass of living organisms.