The first ionisation energies of the elements of the transition series.

Options

A. Increases as the atomic number increases
B. Decreases as the atomic number increases
C. Do not show any change as the addition of electrons takes place in the inner `(n-1)` d-orbitals.
D. None of these

Explanation

To analyze the first ionization energies of the elements in the transition series, we can follow these steps:

### Step 1: Understand the Transition Series
The transition series consists of elements in the d-block of the periodic table, specifically from Scandium (Sc, atomic number 21) to Zinc (Zn, atomic number 30). These elements have partially filled d-orbitals.

**Hint:** Familiarize yourself with the elements in the transition series and their atomic numbers.

### Step 2: Consider the Electron Configuration
The transition metals have their outermost electrons in the s and d orbitals. For example, Sc has the electron configuration [Ar] 3d¹ 4s². As we move across the series, electrons are added to the d-orbitals.

**Hint:** Write down the electron configurations of the first few transition metals to see the pattern.

### Step 3: Analyze Shielding Effect
In transition metals, the d-electrons provide poor shielding for the outermost s-electrons. As we move across the series, the number of protons in the nucleus increases, which leads to a higher effective nuclear charge (Z effective) experienced by the outermost electrons.

**Hint:** Remember that poor shielding means that the outer electrons feel a stronger attraction to the nucleus.

### Step 4: Observe Atomic Size Trend
As the effective nuclear charge increases, the atomic size tends to decrease. This is because the increased positive charge in the nucleus pulls the electrons closer, reducing the atomic radius.

**Hint:** Think about how increased nuclear charge affects the attraction between the nucleus and the electrons.

### Step 5: Determine Ionization Energy Trend
Since ionization energy is the energy required to remove an electron from an atom, and with the increasing effective nuclear charge and decreasing atomic size, the first ionization energy will increase as we move from left to right across the transition series.

**Hint:** Recall that higher ionization energy means it is harder to remove an electron, which correlates with a stronger attraction to the nucleus.

### Conclusion
Thus, the trend for the first ionization energies of the transition series is that they **increase** as the atomic number increases.

**Final Answer:** The first ionization energies of the transition series increase as the atomic number increases.

---