The energy change accompanying the addition of an electron to a gaseous atom is called

Here are the solutions to the questions:

25. The energy change accompanying the addition of an electron to a gaseous atom is called

• This process is defined as the electron affinity. It is the energy change when an electron is added to a neutral atom in the gaseous state to form a negative ion.
• a) first ionization energy: Energy to remove the first electron.
• b) second ionization energy: Energy to remove the second electron.
• c) electron affinity: Energy change when an electron is added.
• d) electronegativity: A measure of the tendency of an atom to attract a bonding pair of electrons.
• The correct option is (c).

26. Four elements P, Q, R and S have atomic numbers of 4, 10, 12 and 14 respectively. Which of these elements is a noble gas?

• Let's identify the elements based on their atomic numbers:
  • P: Atomic number 4 is Beryllium (Be).
  • Q: Atomic number 10 is Neon (Ne).
  • R: Atomic number 12 is Magnesium (Mg).
  • S: Atomic number 14 is Silicon (Si).
• Noble gases are elements in Group 18 of the periodic table, characterized by a full outermost electron shell. Neon (Ne) is a noble gas.
• The correct option is (b).

27. $X_{(g)} \rightarrow X_{(g)}^{+}$ The type of energy involved in the above transformation is

• This equation shows a gaseous atom ($X_{(g)}$) losing an electron to form a gaseous positive ion ($X_{(g)}^{+}$). This process is known as ionization.
• a) ionization energy: The energy required to remove an electron from a gaseous atom or ion.
• b) sublimation energy: Energy required to change a substance from solid to gas.
• c) lattice energy: Energy released when gaseous ions combine to form an ionic solid.
• d) electron affinity: Energy change when an electron is added to a gaseous atom.
• The correct option is (a).

28. Which of the following is arranged in order of increasing electronegativity?

• Electronegativity generally increases from left to right across a period in the periodic table. The elements listed (Sodium, Magnesium, Aluminum, Phosphorus, Chlorine) are all in Period 3.
• Their order in Period 3 is: Na (Group 1) < Mg (Group 2) < Al (Group 13) < P (Group 15) < Cl (Group 17).
• Therefore, the order of increasing electronegativity for these elements is Na < Mg < Al < P < Cl.
• Let's check the options:
  • (a) chlorine, aluminum, magnesium, phosphorus, sodium: This is not in increasing order.
  • (b) sodium, aluminum, phosphorus, chlorine: This sequence (Na < Al < P < Cl) correctly shows increasing electronegativity for the listed elements.
  • (c) chlorine, phosphorus, magnesium, aluminum, sodium: This is not in increasing order.
  • (d) sodium, chlorine, phosphorus, magnesium, aluminum: This is not in increasing order.
• The correct option is (b).

29. Four elements P, Q, R, and S, have 1, 2, 3, and 7 electrons in their outermost shells respectively. The element which is unlikely to be a metal is

• Metals typically have 1, 2, or 3 valence electrons and tend to lose these electrons to form positive ions.
• Non-metals typically have 4, 5, 6, 7, or 8 valence electrons (excluding hydrogen and helium) and tend to gain or share electrons.
• Based on the number of outermost electrons:
  • P: 1 electron (likely a metal, e.g., alkali metal).
  • Q: 2 electrons (likely a metal, e.g., alkaline earth metal).
  • R: 3 electrons (likely a metal, e.g., aluminum).
  • S: 7 electrons (likely a non-metal, e.g., halogen).
• Therefore, element S, with 7 valence electrons, is most unlikely to be a metal.
• The correct option is (d).