Answer:
The part that completes the nuclear equation is:

Explanation:
<h2>A) Preliminar explanation</h2>
The <em>nuclear equation</em> represents a nuclear reaction: the change of the nucleus of an atom.
The given equation represents an actinium atom releasing an alpha particle.
This is the meaning of each part of the equation:
- Ac is the chemical symbol of actinium
- The superscript to the left of the chemical symbol is the mass number of the atom (number of protons plus number of neutrons). The mass number is 225.
- The subscript to the left of the chemical symbol is the atomic number of the atom (number of protons). The atomic number is 89.
is the symbol of the alpha particle. It is an atom of helium- The mass number is 4
- The atomic number is 2
<h2>B) Solution</h2>
To <em>complete the nuclear equation </em>you must do two balances: mass number balance and atomic number balance.
<u>i) Mass number balance</u>
- 225 = A + 4 ⇒ A = 225 - 4 = 221
<u>ii) Atomic number balance</u>
- 89 = Z + 2 ⇒ Z = 89 - 2 = 87
Therefore, the mass number of the unknown atom is 221, and the atomic number is 87.
From a periodic table, the element with atomic number 87 is francium, Fr.
Now, you have the chemical symbol, the atomic number, and the mass number of the unknown atom, which lets you to write the atom that completes the <em>nuclear equation</em>.

Effect of temperature.
"If the temperature of the substance is increased then the rate of chemical reaction is also increased because the kinetic energy is greater."
Effect of surface area.
"If the surface area is increased then the rate of reaction is increased because there will be more active sites for the reaction to occur.
The speed of sound at sea level is 340.29 m/s (meters per seconds).
The force is reasonable for making fusion possible in the Sun is heat energy.
<h3>What is nuclear fission and fusion?</h3>
When the slow moving neutrons are bombarded with the heavy radioactive nuclei, the product is the more number of neutrons are produced with the large amount of energy. This multiplying process is called nuclear fusion.
The amount of energy produced in such a reaction can be calculated using the equivalence of mass and energy relationship.
E = mc²
The same happens in nuclear fusion where large amount of energy is needed to make more heavy nuclei.
Thus, fusion requires heat energy to continue the reaction.
Learn more about nuclear fusion and fission.
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Answer: If there is a higher friction, the opposition force is higher so that it can reduce our speed. So, a factor that affects friction is the roughness or smoothness of the surface of the object. In comparison of the table with the fabric, the fabric will have a more opposition force. As the surface of the fabric is usually rougher than the surface of a smooth table. As there is more friction on a fabric, we will feel more opposition force on our finger tip.
Hope it helped! :>