A canyon would be considered a physical characteristic of the earth because its not man made
Nonane because the molecule contains 9 carbon atoms without any side branches (Non-) and because it only contains single C-C bonds so it is an alkane (-ane).
I don’t know lol but it has high levels of calcium and magnesium which can cause limescale
number of different pairs the teacher can choose= nCr (18+14, 2)=496
no. of opposite gender pairs possible= 14 (since there are only 14 boys)
probability = 14/496= 7/248