Copper does not react with cold water, hot water, or steam. However, iron reacts with steam. If the hot water tanks are made of steel (an alloy of iron), then iron would react vigorously with the steam formed from hot water.
\(3Fe\) + \(4H_2O\) \(→\) \(Fe_3O_4\) + \(4H_2\)
(Iron) (Steam) (Iron(II,III)oxide (Hydrogen)
That is why copper is used to make hot water tanks, and not steel.
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.
