Scientists used to believe that chemical reactions fueled the sun. Why did this lead them to believe that the sun was very young?

The simple answer is that the sun, like all stars, is able to create energy because it is essentially a massive fusion reaction. Scientists believe that this began when a huge cloud of gas and particles (i.e. a nebula) collapsed under the force of its own gravity – which is known as Nebula Theory.

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Because the is live for so long.

Explanation:

the child will have heterozygous dominant chromosomes as characters of his father are dominant over the characters of his mother.

the child is heterozygous

"the periodic table is arranged in order of atomic number."