Which of the following is the definition of Avogadro's constant? What is the empirical formula for C6H12O6? What technique is used to determine the atomic and molecular structure of a crystal?

The number of particles in 1 mole of any substance is defined as Avogadro's constant, which is approximately $6.022 \times 10^{23}$ particles/mol.

• A Molar mass is the mass of one mole of a substance.
• B Avogadro's constant is the number of particles in one mole.
• C Atomic mass unit is a unit of mass used to express atomic and molecular weights.
• D Relative atomic mass is the ratio of the average mass of atoms of an element to $\frac{1}{12}$ of the mass of an atom of carbon-12.

The correct option is B.

$$\boxed{\text{B}}$$

The empirical formula is the simplest whole-number ratio of atoms in a compound. For the molecular formula $\text{C}_6\text{H}_{12}\text{O}_6$, we find the greatest common divisor (GCD) of the subscripts 6, 12, and 6, which is 6.
Divide each subscript by 6:
$\text{C}_{\frac{6}{6}}\text{H}_{\frac{12}{6}}\text{O}_{\frac{6}{6}} = \text{C}_1\text{H}_2\text{O}_1$
The empirical formula is $\text{CH}_2\text{O}$.

The correct option is A.

$$\boxed{\text{A}}$$

X-ray diffraction (XRD) is a technique used to determine the atomic and molecular structure of a crystal. It reveals the crystal structure, including lattice parameters, and the arrangement of atoms within the crystal.

• A Electronic configuration of atoms is determined by quantum mechanics and spectroscopic methods.
• B Crystal structure and lattice parameters are directly determined by XRD.
• C Molecular weight of compounds is determined by techniques like mass spectrometry.
• D Chemical composition is determined by elemental analysis.

The correct option is B.

$$\boxed{\text{B}}$$

Dehydration of ethanol ($\text{CH}_3\text{CH}_2\text{OH}$) at $180^\circ\text{C}$ in the presence of a strong acid (like concentrated sulfuric acid) leads to intramolecular dehydration, forming an alkene.
$\text{CH}_3\text{CH}_2\text{OH} \xrightarrow{\text{conc. H}_2\text{SO}_4, 180^\circ\text{C}} \text{CH}_2=\text{CH}_2 + \text{H}_2\text{O}$
The product is ethene.

The correct option is A.

$$\boxed{\text{A}}$$

Methane ($\text{CH}_4$) has a central carbon atom bonded to four hydrogen atoms. The carbon atom forms four single bonds and has no lone pairs. According to VSEPR theory, this leads to a tetrahedral geometry. To accommodate four single bonds, the carbon atom undergoes $\text{sp}^3$ hybridization.

The correct option is C.

$$\boxed{\text{C}}$$

The industrial preparation of ammonia is known as the Haber-Bosch process. The balanced chemical equation for this reaction is:
$\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g})$
From the stoichiometry, 1 mole of nitrogen reacts with 3 moles of hydrogen. Therefore, the ratio of nitrogen to hydrogen is 1:3.

The correct option is A.

$$\boxed{\text{A}}$$

This question involves Raoult's Law, which states that the vapor pressure of a solvent above a solution is equal to the mole fraction of the solvent multiplied by the vapor pressure of the pure solvent.
Given:
Vapor pressure of pure water ($P^\circ_{\text{water}}$) = $23.8 \text{ mmHg}$
Moles of glucose ($n_{\text{glucose}}$) = $1 \text{ mole}$
Moles of water ($n_{\text{water}}$) = $10 \text{ moles}$

First, calculate the total moles in the solution:
$n_{\text{total}} = n_{\text{glucose}} + n_{\text{water}} = 1 \text{ mole} + 10 \text{ moles} = 11 \text{ moles}$

Next, calculate the mole fraction of water ($X_{\text{water}}$):
$X_{\text{water}} = \frac{n_{\text{water}}}{n_{\text{total}}} = \frac{10 \text{ moles}}{11 \text{ moles}} = \frac{10}{11}$

Now, apply Raoult's Law to find the vapor pressure of the solution ($P_{\text{solution}}$):
$P_{\text{solution}} = X_{\text{water}} \times P^\circ_{\text{water}}$
$P_{\text{solution}} = \frac{10}{11} \times 23.8 \text{ mmHg}$
$P_{\text{solution}} \approx 0.90909 \times 23.8 \text{ mmHg}$
$P_{\text{solution}} \approx 21.636 \text{ mmHg}$

Rounding to one decimal place, the vapor pressure of the solution is approximately $21.6 \text{ mmHg}$.

The correct option is B.

$$\boxed{\text{B}}$$

Transition metals often form colored compounds due to the presence of partially filled d-orbitals. When ligands approach the central metal ion, the d-orbitals split into different energy levels. Electrons can absorb energy (from visible light) and transition from a lower energy d-orbital to a higher energy d-orbital. This process is called d-d transition. The color observed is the complementary color of the light absorbed.

The correct option is D.

$$\boxed{\text{D}}$$

The thermal stability of Group 2 carbonates increases down the group. This is because as you go down the group, the size of the Group 2 cation ($\text{Be}^{2+}, \text{Mg}^{2+}, \text{Ca}^{2+}, \text{Sr}^{2+}, \text{Ba}^{2+}$) increases.
A larger cation has a lower charge density and therefore a lower polarizing power. A cation with lower polarizing power is less effective at distorting the electron cloud of the large carbonate anion ($\text{CO}_3^{2-}$). Less distortion means the carbonate ion is more stable and less likely to decompose into $\text{CO}_2$ and a metal oxide upon heating.

The correct option is D.

$$\boxed{\text{D}}$$

Halogenoalkanes (alkyl halides, R-X) undergo nucleophilic substitution reactions with aqueous sodium hydroxide ($\text{NaOH}$). The hydroxide ion ($\text{OH}^-$) acts as a nucleophile, replacing the halogen atom (X).
$\text{R-X} + \text{NaOH}(\text{aq}) \rightarrow \text{R-OH} + \text{NaX}$
The product formed is an alcohol.

The correct option is D.

$$\boxed{\text{D}}$$

In mass spectrometry, the molecular ion peak (often denoted as $\text{M}^+$ or $\text{M}^+\cdot$) corresponds to the intact molecule that has lost one electron. The mass-to-charge ratio ($\text{m/z}$) of this peak directly gives the molecular mass of the compound.

• A Fragment mass refers to the mass of smaller ions formed by the fragmentation of the molecular ion.
• B Isotope abundance can be determined from the relative intensities of peaks around the molecular ion peak (e.g., M+1, M+2 peaks).
• C Molecular mass is directly given by the molecular ion peak.
• D Bond energy is a thermodynamic property and is not directly measured by mass spectrometry.

The correct option is C.

$$\boxed{\text{C}}$$