Calcium reacts with oxygen to form calcium oxide (CaO), which has a high melting point. Additionally, calcium oxide is soluble in water, forming a basic solution (calcium hydroxide, Ca(OH)₂).
Therefore, the correct answer is (A): calcium.
On the day of her examination, Riya sharpened her pencil from both ends as shown below. 
The diameter of the cylindrical and conical part of the pencil is 4.2 mm. If the height of each conical part is 2.8 mm and the length of the entire pencil is 105.6 mm, find the total surface area of the pencil.
