Question

Atomic number of element with lowest first ionisation enthalpy is:

• A. 32
• B. 19
• C. 35
• D. 87

Hint:

Alkali metals at the bottom of their group, such as Francium, have the lowest ionization energies because the outermost electron is in a higher energy level and is less tightly bound to the nucleus.

Answer 1

The Correct Option is D

Step 1: Understand ionization energy trends.
Ionization energy is the energy required to remove an electron from an atom in its gaseous state.
The first ionization energy decreases as we move down a group because the atomic size increases, making it easier for an electron to be removed.
Conversely, ionization energy increases as we move across a period from left to right because the nuclear charge increases, which makes it harder to remove an electron.
Step 2: Identify the correct group of elements.
The question asks for the element with the lowest first ionization enthalpy.
Alkali metals (Group 1 elements) typically have the lowest ionization energies in the periodic table because they have a single electron in their outer shell, and they tend to lose that electron easily.
Step 3: Consider the position of the elements in the periodic table.
Element with atomic number 19 is Potassium (K), an alkali metal.
Element with atomic number 32 is Germanium (Ge), a metalloid.
Element with atomic number 35 is Bromine (Br), a halogen.
Element with atomic number 87 is Francium (Fr), an alkali metal and the heaviest element in the alkali metal group.

Step 4: Compare the ionization energies.
The ionization energy is lowest for Francium (atomic number 87) because it is at the bottom of the alkali metal group, and the outermost electron is farthest from the nucleus, making it the easiest to remove.