The right answer is D - mass.
Whenever the fuel is being used up, a star explodes and the energy leakage from a star's core ceases.
Explanation:
The dying star expands in the "Red Giant," before even the inevitable collapse starts, due to nuclear reactions just outside of the core.
It becomes a white dwarf star when the star has almost the same density as the Sun. If it's much larger, a supernova explosion could take place and leave a neutron star away. However, if it is very large–at least three times the Sun's mass–the crumbling core of the star, nothing will ever stop it from crumbling. The star is imploding into a black hole, an endless gravitational loop in space.
Thallium has got 81 protons
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CuCl2+F2—>CuF2+Cl2.
This is a single replacement because there is one compound and one element. Picture Cu as ‘A’ Cl2 as ‘B’ and F2 as ‘C.’ So AB+C—>AC+B. A and B “broke up” and that resulted to A going with C to create the compound CuF2 leaving Cl2 alone.
