Conduction - by touch
Convection - hot air rises, cold air sinks
Insulation - to insulate or capture heat
Radiation - by waves
Direct contact means touch, therefore the answer would be conduction.
The error caused will lower the number of moles when he did not do the second heating.This question is related to the empirical formula.
<h3>What is Empirical formula ?</h3>
A formula giving the proportions of the elements present in a compound but not the actual numbers or arrangement of atoms.
The empirical formula is the simplest ratio of atoms in a given compound.
we know that heating is used to eliminate most of the water molecules which are attached to the compound in the question, it's given that the second heating was not performed by the students.
This means that there are still some water molecules attached to the compound. This will imply that higher mass will be calculated for the compound because the water molecules are also considered.
So now, if we look at the calculation for the number of moles of water in this, we can say that this will be lower than the actual amount.
This is because there are some unaccounted moles of water which are still attached to the compound and these will be accounted in the compound mass rather than the waters. Therefore, the number of moles will be lower.
Hence, The error caused will lower the number of moles when he did not do the second heating.
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if da ceiling in a square that means it has four sides. If each side is 39 feet and there are four sides you would multiply 39 times 4 which equals 156. If one can of paint can cover 169 ft.² and the ceiling is only 156 ft.² then you would only need 1 CAN OF PAINT.
Answer:

Explanation:
When we are given Bohr models, we will be given a circle with rings surrounding it. The circle in the center of the model represents the nucleus, which contains the neutrons and the protons. The rings will have spherical structures that are attached to them in an orderly fashion - these model the electrons of an atom.
- Protons are positively-charged subatomic particles that also identify the atom's chemical identity and atomic number. Using the number of protons, we are able to identify the element.
- The neutrons are the neutrally-charged subatomic particles that give an atom its weight. When you look at a traditional periodic table, you'll see that the square that houses an element has its symbol, atomic number, and atomic mass. The atomic mass is equivalent to the sum of the protons and neutrons.
- Electrons are negatively-charged subatomic particles that give an atom its overall charge. In order for an atom to be stable and neutral, the electrons <u>must</u> equal the protons. Otherwise, we have an unstable atom called an ion with either a positive or a negative charge. This is dependent on whether an atom has gained or lost electrons.
When we reference the model, we will see that there are 13 "p" and 14 "n" within the green circle. The "n" refers to <em>neutrons </em>and the "p" refers to <em>protons</em>. We can also count the red spheres and make quick observations about these: there are 2 red spheres on the innermost ring - for simplicity reasons, we will title this ring as r = 1. There are 8 red spheres on the middle ring - this ring will be titled r = 2. Finally, we can see that there are 2 more electrons in the outermost ring - this ring will be titled r = 3.
Now, because we have 13 protons, we know that the protons are equivalent to the atomic number.
- If we check the periodic table, we will see that Silicon (Si) has an atomic number of 14. This doesn't match the number of protons, so we can rule out that a silicon atom is not the element shown.
- When we use the same process and check aluminum, we discover that Aluminum (Al) has an atomic number of 13. Since the number of protons and the atomic number are equal, we can conclude that this is the element.
- If we check Helium (He), we see that it has an atomic number of 2, so this is definitely not our element in question.
Now that we have concluded that Aluminum is our element, we can check this to be sure. If we use the formula m = n + p (where m is the atomic mass, n is the neutrons, and p is the protons), we can check to be sure we have selected the right element.
The given mass of aluminum on the periodic table is 26.982 atomic mass units. We round to the nearest integer when it comes to this, so we round 26.982 up to 27 even.
Now that we have determined the atomic mass and we are given the number of both protons and neutrons, we can act as if we weren't given the amount of neutrons and only the mass and amount of protons. We can then use the equation to solve for the amount of neutrons and check that the selection we made is correct.
<u>Steps</u>
- Substitute 27 for <em>m</em> and 13 for <em>p</em>.
- Subtract 13 from both sides to isolate the <em>n</em> and place the constants on the same side of the equation.
- Combine like terms by taking the appropriate operations (in this case, this is subtracting 13 from 27).
- Finally, because we are solving for <em>n</em>, you can reverse the equation (place the constant on the right and place the variable on the left; i.e., 72 = x → x = 72).

The work we just performed will allow us to confirm that because we solved for <u>14 neutrons</u>, Aluminum (Al) is indeed the element represented by the model.
Hope this helps! :)
Answer:
As we go down the group, the atom gets bigger. The bigger the atom, the further away the last electron. Therefore, the attraction between the nucleus and the last electron gets weaker. This makes it easier for the atom to give up the electron which increases its reactivity.
Explanation: