Please what the element it is

100mg magnesium reacts with 20ml of 1.0m hcl

Write the symbol for every chemical element that has atomic number greater than 3 and atomic mass less than 12.0 u.

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