Where I could publish my theories?​

Which is not true about oxygen-17 and oxygen-18?

This is for my 8th grade science class, i really don’t understand. can someone me? , lol.

Asolid cylinder and a cylindrical shell have the same mass, same radius, and turn on frictionless, horizontal axles. the cylindrical shell has light-weight spokes connecting the shell to the axle. a rope is wrapped around each cylinder and tied to blocks of equal masses that are held the same height above the ground. both blocks are released simultaneously. the ropes do not slip. which block hits the ground first? or is it a tie?