An element is a pure substance
It is called the atomic number. (In physics it can also be called the proton number)
Answer:

Explanation:
magnesium + nitrogen ⟶ Product
13 g 5 g
Mass of product = 13 g + 5 g = 18 g
The product contains 5 g of nitrogen
.

Answer:
chlorophyll
Explanation:
Plants are green because their cells contain chloroplast which have pigment which absorb deep-blue and red light so that the rest of the sunlight spectrum is being reflected, causing the plants to look green.
D. Synthesis cause A + B --> AB
Equation: 2Na + Cl2 --> 2NaCl