Atoms of the same element that have different masses are called

ISOTOPES

Explanation:

As we know that the atoms of same element with different number of protons is known as ISOTOPES

So here we can say that

here in above example the two atoms are same with same atomic number z

but the mass number is different in it

As we know that

mass number = number of proton + number of neutrons

So isotopes must have different number of neutrons present in the nuclei

answer: 802.3 kilo joules of energy represents 191.75 kilo calorie of energy.

explanation:

energy released during combustion of one mole methane = 802.3 kilo joules

if 1 kilo joule = 0.239006   kilo calorie

then ,802.3 kilo joule will be = 802.30.239006 kilo calorie

802.3 kilo joule = 191.75 kilo calorie

hence, the energy in kilo calorie is 191.75 kilo calorie.