why will the color of the sun change from yellow to red when it becomes a giant?

Look up Red Giant and the Sun in the Crash Course Astronomy YouTube videos, he explains things pretty well. I think basically the sun will get cooler and bigger which means more heat but also lower energy (mroe red) light.

Because the sun will be cooler. Red are cooler Suns, blue are hotter Suns.

Why will the color of the sun change from yellow to red when it becomes a giant?

When burning helium the core burns brighter. That pushes the surface further out. Since the surface is further out it is cooler. Red is the cooler color.

When the sun will reach the end state of its life,the size of sun will increase means only the outer layer will increase in size. Now the sun will be having vary large size but the temperature of sun at the surface will be much smaller as compared to the earlier time. Since the smaller temperature corresponds to the red color and higher temperature corresponds to the blue color. The color of sun will become reddish as the size will increase.

Note that only the surface temperature has decreased not the core temperature. The core temperature increases during the end time of star.

the color of the sun will only change colors when it is dying. in resemblance to a fire it will change colors depending on how hot the flame is, once the sun changes red it may expand and form what is called a red giant, which is the stage before it dies and becomes a white dwarf and dies out or will implode and form a black hole sucking everything in its reach into it and killing it.

All predictions are nonsense because they are somebody's imagination. Astronomers think the sun is powered by fusion, and it's not. Fusion implies the inside is hotter than the outside, and the reverse is true. The Hertzsprung-Russel diagram is based on the same assumption, so generalizations about size and color are also based on imaginations and assumptions.

It will not be producing as much energy even though it will be much larger , it will put out energy on the lower end of the spectrum , red or infrared as opposed to blue for a very hot and energetic star.

Because it's surface area has massively increased

Becasue it will get cooloer in temperature

https://youtu.be/4a0FbQdH3dY

The interior of the sun will heat up, but this will force the outer layers to expand and cool down.

Yellow To Red

because it will get hotter. remember: white is hottest, yellow is the least hot, red is hotter than yellow but colder than blue, and blue is colder than white but hotter than red.