Some Basic Concepts Of Chemistry

Step 1: The cell consists of a zinc electrode and a hydrogen electrode. The EMF of the cell is given by:
Step 2: The potential of the hydrogen electrode is calculated using the Nernst equation:
Step 3: Since and , the hydrogen ion concentration is:
Step 4: Substitute into the Nernst equation:
Step 5: Now calculate the EMF of the cell:
Step 6: By convention, the more positive electrode is considered the cathode. Since the hydrogen electrode has a more positive potential, it is the cathode. The final EMF is positive because the cell spontaneously generates current:

Step 1: For a first-order reaction, the time required to complete a fraction of the reaction is given by: where is the rate constant, is the initial concentration, and is the concentration at time .
Step 2: Let . For 75% completion, :
Step 3: Solve for the rate constant :
Step 4: For 50% completion, :
Step 5: Solve for :

Step 1: Recall that the strength of oxy-acids depends on the electronegativity of the central atom and its ability to stabilize the conjugate base.
Step 2: In group 15, electronegativity decreases down the group:
Step 3: Higher electronegativity of the central atom increases the acidic strength of the oxy-acid.
Step 4: Therefore, the decreasing order of acidic strength is:
Step 5: Hence, option (C) is correct.

Step 1: Orbital angular momentum of an electron is given by: where is the azimuthal quantum number.
Step 2: For a -orbital:
Step 3: Substitute the value of :
Step 4: Hence, the orbital angular momentum of an electron in a -orbital is:

Step 1: The orbital is oriented along the -axis.
Step 2: For a orbital, the YZ plane (where ) is a nodal plane.
Step 3: In a nodal plane, the wave function , hence the probability density:
Step 4: Therefore, the probability of finding an electron in the YZ plane for a orbital is:

Step 1: Vapour density (VD) is related to molar mass as:
Step 2: Given atomic ratio of carbon and hydrogen is . Hence, the empirical formula is:
Step 3: Empirical formula mass of :
Step 4: Determine the molecular formula factor:
Step 5: Molecular formula:

Step 1: Energy of electron in the orbit of hydrogen atom is given by:
Step 2: Ground state corresponds to . First excited state corresponds to . Second excited state corresponds to .
Step 3: Substitute in the formula:
Step 4: Hence, the energy of electron in the second excited state is:

Step 1: Coloured discharge tubes used in advertisements are filled with noble gases.
Step 2: Each gas gives characteristic color due to electronic transitions.
Step 3: Neon is most commonly used because: - It emits intense orange-red light, - It works at low pressure and voltage, - It is chemically inert and inexpensive.
Step 4: Other gases are used rarely for special shades; the standard is neon.

Step 1: Identify the type of infection. Throat infections are generally caused by bacterial pathogens such as \textit{Streptococcus} species.
Step 2: Recall the therapeutic use of the given drugs.
Quinine — used in the treatment of malaria.
Piperazine — used as an anthelmintic (for intestinal worms).
Sulpha drugs (e.g., sulphanilamide) — act as antibacterial agents, commonly used in throat and other bacterial infections.
Isonicotin hydrazide (INH) — used in the treatment of tuberculosis.
Step 3: Select the appropriate drug. Since throat infection is bacterial, the suitable drug is a sulpha drug.
Hence, the correct answer is

Step 1: Analyse option (A). Proteins are polymers of -amino acids linked by peptide bonds. On hydrolysis, proteins yield only -amino acids.
Step 2: Analyse option (B). Amino acids that can be synthesized by the human body are called non-essential amino acids.
Step 3: Analyse option (C). Although there are 20 common amino acids found in proteins, all of them are not essential. Essential amino acids are those that \emph{cannot} be synthesized by the body and must be obtained from diet. Their number is much less than 20.
Step 4: Analyse option (D). In Fischer projection:
L-amino acids have the group on the left side
D-amino acids have the group on the right side
Hence, the incorrect statement is

Step 1: Check statement 1 (Isotopes). Isotopes are atoms with:

Same atomic number
Different mass number
Hence, statement (1) is correct. Step 2: Check statement 2 (Isobars). Isobars are atoms with:

Same mass number
Different atomic number
But the statement says “same number of neutrons”, which is incorrect. Hence, statement (2) is incorrect. Step 3: Check statement 3 (Isotones). Isotones are atoms with:

Same number of neutrons
Different atomic number
But the statement says “same mass number”, which is incorrect. Hence, statement (3) is incorrect. Step 4: Final conclusion. Only statement (1) is correctly matched.

Step 1: In pure water at 25 C: Step 2: Calculate pH: Hence, pure water is neutral.

Step 1: Given concentration of NaOH After dilution by 100 times: Step 2: Consider contribution of water. Pure water contributes: Total hydroxide ion concentration: Step 3: Calculate pOH: Step 4: Calculate pH: Since the pH is slightly greater than 7, it lies between 7 and 8.