Analyze the provided experimental setups and flowcharts to identify substances, describe collection methods, and relate boiling points to gases.

Here are the solutions to the questions:

26. The set-up below was used to prepare and collect a dry sample of hydrogen sulphide. Study it and answer the questions that follow. a) Name solid M, and state it colour Solid M: $\boxed{\text{Iron (II) sulphide}}$ Colour: $\boxed{\text{Black}}$

    b) Complete the diagram above to show how dry sample of the gas is collected.
    (Since I cannot draw, I will describe the completion of the diagram.)
    The delivery tube from the conical flask (where hydrogen sulphide is generated) should lead into a drying bottle or U-tube containing an appropriate drying agent such as anhydrous calcium chloride. After passing through the drying agent, the gas should be collected in a gas jar by downward delivery of air (upward displacement of air), as hydrogen sulphide is denser than air. The delivery tube should extend to the bottom of the gas jar.

27. Study the flow chart below and answer the questions that follow. a) (i) Name the substances removed in steps I, II and III I: $\boxed{\text{Dust}}$ II: $\boxed{\text{Carbon dioxide}}$ III: $\boxed{\text{Water vapour}}$

    (ii) Name the gases obtained with respect to their boiling points.
    $-196^\circ\text{C}$: $\boxed{\text{Nitrogen}}$
    $-186^\circ\text{C}$: $\boxed{\text{Argon}}$
    $-183^\circ\text{C}$: $\boxed{\text{Oxygen}}$

    b) With the aid of labeled diagrams explain how you would show that for rusting to occur, oxygen is necessary.
    (Since I cannot draw, I will describe the experimental setup and observations.)
    Setup:

    1. Test tube A: Place a clean iron nail in boiled distilled water (to remove dissolved oxygen). Add a layer of oil on top to prevent atmospheric oxygen from dissolving back into the water.
    2. Test tube B: Place a clean iron nail in tap water (which contains dissolved oxygen).
    3. Test tube C: Place a clean iron nail in a test tube containing anhydrous calcium chloride (to absorb moisture) and stopper it. This provides dry air. Observations:
    • In Test tube A, the iron nail does not rust.
    • In Test tube B, the iron nail rusts.
    • In Test tube C, the iron nail does not rust. Explanation: Rusting occurs only in Test tube B, where both water and oxygen are present. Test tube A lacks oxygen, and Test tube C lacks water. This demonstrates that both oxygen and water are necessary for rusting to occur.

28. The grid below represents periodic table. Study it and answer the questions that follow. The letters do not represent the actual symbols of the elements. The question is incomplete as there are no questions provided to answer regarding the periodic table grid.