197- The work functions of metals A and B are $4\text{eV}$ and $2\text{eV}$ respectively, and light with a wavelength of $200$ nanometers shines on both metals. The fastest photoelectrons separated from metal B compared to the fastest photoelectrons separated from metal A are how many times faster? $\left(c = 3\times10^{8}\ \dfrac{\text{m}}{\text{s}}\ \text{ and }\ h = 4\times10^{-15}\ \text{eV.s}\right)$
\[ \frac{1}{2} \quad (4) \qquad\qquad \frac{\sqrt{r}}{r} \quad (3) \qquad\qquad \sqrt{r} \quad (2) \qquad\qquad r \quad (1) \]

198- In the hydrogen atom, the electron energy at one level is $-0.85\text{ eV}$. If the electron transitions from this level to the level where the electron energy is $-3.4\text{ eV}$, the speed will be how many times? $\left(E_R = 13.6\text{ eV}\right)$
\[ 4 \quad (4) \qquad\qquad 2 \quad (3) \qquad\qquad \frac{1}{2} \quad (2) \qquad\qquad \frac{1}{4} \quad (1) \]

199- When we add a three-valent impurity like aluminum (similar to silicon) to a semiconductor, in terms of capacity:

1. In addition to the empty bands related to electrons that have gone to the conduction band, one electron is also added for each aluminum atom.
2. In addition to the empty bands related to electrons that have gone to the conduction band, one hole is also created for each aluminum atom.
3. The number of holes will be less than the number of electrons.
4. Equal numbers of electrons and free holes will be created.

200- Which statement about $^{235}$U and $^{238}$U is not correct?

1. The number of neutrons in $^{238}$U is greater.
2. Both have the same number of protons.
3. Both have the same chemical properties.
4. $^{238}$U, $0.72\%$ forms natural uranium.

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201. The number of unpaired electrons in atom $_{16}$S with the number of unpaired electrons in which atom is equal?
(1) $_{24}$Cr (2) $_{26}$Fe (3) $_{28}$Ni (4) $_{31}$Ga

202. The second ionization energy of which element, compared to the others given, is greater?
(1) $_{11}$Na (2) $_{5}$B (3) $_{4}$Be (4) $_{9}$F

203. Which statement about the periodic table of elements is correct?

1. Liquid elements (under standard conditions) have non-metallic properties.
2. Some elements of the sixth period of the periodic table have not yet been discovered.
3. Two elements $_{22}$Z and $_{22}$X are intermediate elements and belong to the same group.
4. Lanthanides and actinides are placed in the sixth and seventh periods of the periodic table, respectively.

204. Which statement about the reaction of alkali metals with water is correct?

1. The reaction rate increases with increasing their atomic number.
2. From the reaction of each mole of them with water, $22.4\,\text{L}$ of gas is produced at STP conditions.
3. A flame is observed from the reaction of some of them with water, resulting from combustion.
4. After the reaction of one gram of each of them with pure water, the pH of the resulting solutions is equal.

205. Hydrogen sulfate and hydrogen phosphate ions are similar in which respect?
$$(H = 1,\ O = 16,\ P = 31,\ S = 32 : \text{g.mol}^{-1})$$

1. Percentage of oxygen (2) Number of negative electric charge units
2. Number of central atom oxidation (4) Number of central atom electron pairs

206. The sum of the electric charges of cyanide, nitrate, phosphate, chlorate, and permanganate ions with the number of oxygen atoms in these ions — what is the chemical formula of these ions?
(1) 5 (2) 6 (3) 7 (4) 8

207. Which two compounds are isomers (isomers)?

1. Cyanamide ; propylamine (2) 1-butanol ; diethyl ether
2. Acetic acid ; formaldehyde (4) Dinitrogen tetroxide ; nitrogen dioxide

208. The number of shared electron pairs in the molecule of which two compounds is not equal?
(1) $SO_2$ , $HCN$ (2) $PF_5$ , $HNO_3$
(3) $HCOOH$ , $CH_3OH$ (4) $H_2CO_3$ , $N_2O_4$

209. The number of nonbonding electron pairs on the central atom in which ion is equal to the number of nonbonding electron pairs on the central atom of $\text{BrO}_2^-$?
(1) $NCS^-$ (2) $NO_2^-$ (3) $PCl_4^-$ (4) $BF_4^-$
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210 -- How many of the following statements are correct?

• From acetylene, many organic compounds can be prepared.
• From the reaction of water with calcium carbide, acetylene gas is obtained.
• Acetylene is the simplest alkyne and its molecule is linear and nonpolar.
• Polypropylene is part of the synthesized compounds and is used in carpet and rug production.

(1) 1 (2) 2 (3) 3 (4) 4

211 -- How many of the following statements about the compound whose molecular structure is shown below are correct?
[Figure: Molecular structure with HO, C=O, NH$_2$, and NH$_2$ groups]

• It has amphoteric properties.
• It can be used in the preparation of polyamides.
• Part of its structure resembles alpha -- amino acids.
• The number of carbon atoms in its molecule equals the number of hydrogen atoms in the molecule.

(1) 1 (2) 2 (3) 3 (4) 4

212 -- The sum of the stoichiometric coefficients of the reactants in the balanced equation: $$\text{C}_2\text{H}_5\text{NH}_2 + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O} + \text{N}_2$$ after balancing, which option is correct?
(1) 22 (2) 24 (3) 15 (4) 17

213 -- Considering the number of atoms forming one molecule of a chemical substance (according to the figure below), how many of the following statements are correct? ($\text{H} = 1,\ \text{C} = 12,\ \text{O} = 16\ \text{: g.mol}^{-1}$)
[Figure: Ball-and-stick model showing C, H, and O atoms]

• It is benzaldehyde molecule.
• It is a chain compound.
• Approximately 35.56\% of its mass is oxygen.
• The ratio of the mass of carbon atoms to the mass of hydrogen atoms in it is 13/5.

(1) 1 (2) 2 (3) 3 (4) 4

214 -- Based on the reaction: $3\text{Cu(s)} + 8\text{HNO}_3\text{(aq)} \rightarrow 3\text{Cu(NO}_3)_2\text{(aq)} + 2\text{NO(g)} + 4\text{H}_2\text{O(l)}$, to prepare 14.1 grams of copper(II) nitrate, how many milliliters of 2 molar nitric acid solution are needed? (yield: 80\%)
$$(\text{N} = 14,\ \text{O} = 16,\ \text{Cu} = 64\ \text{: g.mol}^{-1})$$
(1) 125 (2) 100 (3) 50 (4) 25
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215. A chemical substance contains three atoms of chromium in its chemical formula. If $31.2\%$ of this substance is chromium, what is the molar mass of this substance? $(Cr = 52 : \text{g.mol}^{-1})$
(1) $166.7$ (2) $250$ (3) $333.3$ (4) $500$

216. If from the complete combustion of a certain amount of magnesium under standard conditions, 20 grams of magnesium oxide is formed and 300 kilojoules of heat is released, what is the standard $\Delta H$ of formation of magnesium oxide per mole? $(O = 16,\ Mg = 24 : \text{g.mol}^{-1})$
(1) $+300$ (2) $-300$ (3) $+600$ (4) $-600$

217. Which of the following statements about thermal motions is correct?

• It includes rotational and vibrational motions of molecules.
• Transitional motions are observed in all states of matter.
• At a certain temperature, the distribution of vibrational energy of particles of a substance is equal.
• The average thermal motions of a sample of matter are reported as the temperature of that sample.

(1) 1 (2) 2 (3) 3 (4) 4

218. In which reaction is the European (entropy) factor favorable? (Assume STP conditions.)
(1) Preparation of ammonia gas (2) Rusting of iron (3) Combustion of propane (4) Decomposition of nitroglycerin

219. From the decomposition of each gram of ammonium nitrate, according to the reaction (unbalanced):
$$\text{NH}_4\text{NO}_3(s) \rightarrow \text{N}_2(g) + \text{H}_2\text{O}(g) + \text{O}_2(g)$$
$1.5\ \text{kJ}$ of energy is released. If the enthalpy of formation of $\text{H}_2\text{O}(g)$ is $-245\ \text{kJ.mol}^{-1}$, what is the enthalpy of formation of ammonium nitrate per mole?
$(H = 1,\ N = 14,\ O = 16 : \text{g.mol}^{-1})$
(1) $-370$ (2) $+370$ (3) $-440$ (4) $+440$

220. The solubility of potassium nitrate at $42^\circ\text{C}$ is 61 grams per 100 grams of water. To approximately dissolve this many moles of salt, how many liters of water must be added to obtain a saturated solution at this temperature? (Density of water is $1\ \text{g.mL}^{-1}$.)
$(K = 39,\ O = 16,\ N = 14 : \text{g.mol}^{-1})$
(1) $9.04$ (2) $12.08$ (3) $18$ (4) $24$

221. The concentration of sodium ions in a sample of seawater is $10600\ \text{ppm}$. If the density of this water sample is $1.05\ \text{g.mL}^{-1}$, what is the approximate molar concentration of sodium ions?
$(Na = 23 : \text{g.mol}^{-1})$
(1) $0.22$ (2) $0.36$ (3) $0.48$ (4) $0.65$
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