Astronomers have found a planet (called planet X) with the same mass as Earth (5.98x10^24 kg), but it’s radius is only half what the Earth is ( r=3.175x10^6 m). What is the acceleration of gravity on planet X ?

Elements in group viiia (also known as group 18, or the noble gases) have similar properties because they all have a. the same number of electron shells b. full octets c. the same number of valence electrons d. the same number of electrons needed to fill their octet