Q.Identify nuclear fusion reaction
a. 1-1-H + 1-1-H → 2-1-H + 0-1-e
b. 2-1-H + 1-1-H → 3-2-He
c. 3-1-H + 1-1-H → 3-1-H + 1-1-p

Fusing light nuclei requires overcoming their electrostatic repulsion, which needs temperatures of the order 10^8 K.

For two positively charged nuclei to fuse, they must approach close enough for the short-range nuclear force to take over, overcoming the long-range Coulomb repulsion between them. This requires the nuclei to have very high kinetic energy, corresponding to temperatures of the order of 10^7-10^8 K. Among the given choices, 10^8 K is the physically correct order of magnitude (the other options - room temperature, absolute zero, or a tiny fraction of a kelvin - are nowhere close).

Fusion is the opposite of fission: light nuclei join to form a heavier one, and because the binding energy per nucleon is higher for the product, energy is released.

Nuclear fusion is a process in which two light atomic nuclei combine (fuse) to form a single heavier nucleus, releasing energy in the process — because the binding energy per nucleon of the heavier product nucleus is greater than that of the light reactant nuclei (since fusion occurs on the rising part of the binding-energy-per-nucleon vs mass-number curve). Example: $_1^2H + {}_1^3H \rightarrow {}_2^4He + {}_0^1n +$ energy. Fusion of hydrogen into helium is the energy source of the Sun and other stars.

The Sun (and other stars) generate their energy through nuclear fusion — light hydrogen nuclei combining to form helium, releasing enormous energy.

Inside the Sun's core, extremely high temperature (~$1.5\times10^7$ K) and pressure allow light nuclei — mainly protons (hydrogen nuclei) — to overcome their mutual Coulomb repulsion and fuse together. Through the proton–proton chain, four hydrogen nuclei ultimately combine to form one helium-4 nucleus:

$4\,^1_1\text{H} \rightarrow\ ^4_2\text{He} + 2e^+ + 2\nu + \text{energy}$

The mass of the helium nucleus produced is slightly less than the combined mass of the four protons; this mass defect is released as energy (via $E = \Delta m\,c^2$), which powers the Sun's radiation. (Nuclear fission, by contrast, is the splitting of a heavy nucleus like uranium — this occurs in reactors and fission bombs, not in the Sun.)

The required temperatures are too extreme for any laboratory material to confine, since both nuclei are positively charged and repel strongly.

Nuclear fusion requires two positively-charged nuclei to be brought close enough together (within the range of the strong nuclear force, $\sim10^{-15}$ m) to fuse. Since both nuclei are positively charged, they strongly repel each other electrostatically (Coulomb repulsion), and this repulsive barrier increases sharply as they approach each other. To overcome this barrier, the nuclei need extremely large kinetic energies, corresponding to temperatures of the order of $10^7$–$10^8$ K (achieved naturally inside stars, where fusion powers their energy output). At such temperatures, matter exists as a plasma, and no ordinary solid material container can withstand or physically confine it (it would instantly vaporise/melt); controlled fusion instead requires exotic confinement methods (magnetic or inertial confinement), which are extremely difficult and remain a major unsolved engineering challenge. This is why controlled/sustained nuclear fusion is not easily achieved in an ordinary laboratory, even though it is the energy source of stars.

Four protons uniting into a helium nucleus with energy release is nuclear fusion (the solar reaction).

The reaction $4\,{}_{1}^{1}H \rightarrow {}_{2}^{4}He + 2\,{}_{+1}\beta^{0} + Q$ combines four light nuclei (protons) into one heavier nucleus (helium), releasing energy $Q$. Building a heavier nucleus from lighter ones is nuclear fusion — this is the proton–proton cycle that powers the Sun. (Fission, by contrast, is the splitting of a heavy nucleus.)

Solar energy is produced by nuclear fusion of hydrogen into helium.

In the Sun's core, under enormous temperature and pressure, hydrogen nuclei fuse to form helium (the proton–proton cycle). The mass of the helium nucleus is slightly less than the mass of the four protons that formed it; this mass defect Δm is converted into energy according to E = Δm·c². This fusion is the continuous source of the Sun's radiated energy — not fission or chemical reactions.

The Sun's energy is generated by thermonuclear fusion — four protons fuse (via the proton–proton chain) into a helium nucleus, releasing energy because the products are less massive than the reactants ($\Delta E = \Delta m\,c^2$).

Inside the Sun's core, at temperatures of about $1.5\times10^7\,K$ and enormous pressure, hydrogen nuclei (protons) undergo a sequence of nuclear fusion reactions (the proton-proton cycle):

$4\,{}^1_1\text{H} \longrightarrow {}^4_2\text{He} + 2e^+ + 2\nu + \text{energy}$

The mass of the resulting helium-4 nucleus is slightly less than the mass of four protons. This mass defect $\Delta m$ is converted into energy according to Einstein's relation:

$E = \Delta m\,c^2$

This fusion energy, released continuously over billions of years, is what powers the Sun and reaches us as solar energy. It is not nuclear fission (that occurs in reactors, not naturally in the Sun), not simple gravitational contraction (that was an outdated 19th-century hypothesis inadequate to explain the Sun's age/lifetime), and not ordinary chemical burning of hydrogen in oxygen (chemical energy is far too small to sustain solar output).