A pure substance is anything that cannot be broken down or separated by means?

Physical is the blank space

Explanation: Your welcome

Explanation:

An element is a pure substance which cannot be broken down into anything simpler by chemical methods. Most elements consist of a mixture of isotopes and so are not pure substances. Isotopes of an element can be separated by physical methods such as diffusion and mass spectrometry.

568.98

explanation:

its math

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.