Q. Which symbol is opposite to symbol #?
In diagrams I and III, ‘%’ is common and in the same place (top face). Hence, by rule-2 (one common, same place, corresponding opposite), symbol ‘@’ is opposite to symbol ‘#’. Alternatively, in diagrams I and IV, symbols ‘%’ and ‘&’ are common. Hence, by rule-1 (two common, 3rd opposite), symbol ‘@’ is opposite to symbol ‘#’.