The question asks about the trend of melting and boiling points of alkali metals as we move down Group 1 of the periodic table. This trend is determined by the strength of the metallic bonding, which in turn depends on factors like atomic size and the number of delocalized electrons.
Correct Option: D) Decrease. As atomic size increases down Group 1, the metallic bonding becomes weaker due to the increased distance between the nucleus and the delocalized valence electron. Weaker metallic bonds require less energy to break, leading to lower melting and boiling points.
This question tests knowledge about flame tests, a common analytical technique used to identify the presence of certain metal ions based on the characteristic color they impart to a flame. Alkali metals, due to their easily excitable valence electrons, show distinct colors.
Correct Option: C) Golden yellow
This question tests knowledge of flame tests, a common analytical technique used to identify the presence of certain metal ions based on the characteristic colour they impart to a flame. Each metal ion emits light at specific wavelengths when heated in a flame, resulting in a unique colour.
Correct Option: D) Lithium salts impart a characteristic crimson red colour to a flame. This is due to the excitation and subsequent de-excitation of electrons in lithium atoms, emitting light at specific wavelengths corresponding to crimson red.
This question tests knowledge of flame tests, a common analytical chemistry technique used to detect the presence of certain metal ions. When heated in a flame, electrons in the metal ions get excited to higher energy levels. As they fall back to their original energy levels, they emit light of specific wavelengths, resulting in characteristic colours.
Correct Option: C) Lilac (violet) — Potassium salts impart a characteristic lilac (violet) colour to a flame due to the emission of light at specific wavelengths by excited potassium ions.
The question asks why alkali metals and their salts impart characteristic colors to a flame. This phenomenon is known as the flame test and is a fundamental concept in atomic structure and spectroscopy. The explanation lies in how atoms interact with energy, specifically heat from a flame.
B) The heat excites the outer electron, which emits energy as visible light on returning to the ground state. This option accurately describes the process of atomic excitation and subsequent emission of visible light, which is the basis for the characteristic flame colors of alkali metals.
The photoelectric effect is the emission of electrons when light shines on a material. For an alkali metal to be suitable for photoelectric cells, it must exhibit the photoelectric effect with visible light, meaning it should have a low work function. The work function is the minimum energy required to remove an electron from the surface of a metal. Alkali metals have low ionization energies, which generally correlates with a low work function. We need to identify which alkali metal has the lowest work function among the given options.
Correct Option: A) Caesium is the alkali metal with the lowest work function among the given options, making it the most efficient for exhibiting the photoelectric effect with visible light and thus ideal for photoelectric cells.