Where is the energy being transferred from in an endothermic reaction?

When the earth was formed and cooled, why did nickel and iron end up in the center of the earth while basalt and granite ended up in the outer layers

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

Precision can be defined as the o exact center of a data set. o reproducibility of a measured value. o correlation between two variables that are measured in a data set agreement between a measured value and an accepted value.