Which has the least gravitational potential energy? a 25 kg barbell above the head of a weightlifter or a 10 kg barbell resting on the floor

Indicate whether the specified alkyl halides will form primarily substitution products, only elimination products, both substitution and elimination products, or no products when they react with sodium methoxide. 1-bromobutane 1-bromo-2-methylpropane 2-bromobutane 2-bromo-2-methylpropane