Due to which property of an object does it resist any attempt to change its state of motion?

Which one of the following persons is in an inertial frame of reference?

Newton's first law is applicable

$A$ boy travelling in an open car moving at constant velocity throws a ball vertically up into the air. The ball falls

$A$ girl jumps down from a moving bus,along the direction of motion of the bus,tilting slightly forward. She falls on $(a)$ a sheet of ice $(b)$ a patch of glue. Which of the following statements is correct regarding her fall?

Give two points of difference between mass and weight.