What is a observation?

An electrons position cannot be known precisely only it's probability of being in a certain location can be known

Cucl2 + 2nano3 cu(no3)2 + 2nacl what is the percent yield of nacl if 31.0 g of cucl2 reacts with excess nano3 to produce 21.2 g of nacl? 49.7% 58.4% 63.6% 78.7%

In the reaction between a crushed antacid tablet and vinegar what gas is emitted