Both alkali metals and alkaline earth metals are `s-`block elements. They resemble each other in many respects but still there are certain dissimilarities in their properties due to different number of electrons in the valence shell, different atomic radii, ionisation enthalpy, electronegativity, etc.
Like lithium, Be also differs from rest of the alkaline earth metals on account of its small atomic size and high electronetativity. `Be^(2+)`ion is very small and exerts a high polarising effect on any anion associated with it.
The alkaline earth metal which does no directly combine with hydrogen is

Options

A. `Be`
B. `Ca`
C. `Sr`
D. `Ba`

Explanation

To solve the question regarding which alkaline earth metal does not directly combine with hydrogen, we can follow these steps:

### Step 1: Understand the Group Characteristics
Both alkali metals and alkaline earth metals belong to the `s-block` of the periodic table. They have similar properties, but there are significant differences due to their atomic size, ionization enthalpy, and electronegativity.

**Hint:** Remember that the properties of elements in the same group can vary significantly based on their position in the periodic table.

### Step 2: Identify the Alkaline Earth Metals
The alkaline earth metals include:
- Beryllium (Be)
- Magnesium (Mg)
- Calcium (Ca)
- Strontium (Sr)
- Barium (Ba)

**Hint:** Listing the elements helps in comparing their properties.

### Step 3: Analyze Beryllium's Unique Properties
Beryllium is unique among the alkaline earth metals due to its small atomic size and high electronegativity. This leads to a high ionization enthalpy, meaning it requires a lot of energy to remove an electron from beryllium.

**Hint:** Focus on how atomic size and ionization energy affect the ability of an element to react.

### Step 4: Compare with Other Alkaline Earth Metals
As we move down the group from beryllium to barium, the atomic size increases, and the ionization enthalpy decreases. This means that larger alkaline earth metals can more easily lose electrons and thus can combine with hydrogen.

**Hint:** Consider how the size and ionization energy influence the reactivity of the metals with hydrogen.

### Step 5: Conclusion
Since beryllium has a high ionization energy, it does not readily lose electrons to combine with hydrogen. Therefore, it is the alkaline earth metal that does not directly combine with hydrogen.

**Final Answer:** The alkaline earth metal which does not directly combine with hydrogen is **Beryllium (Be)**.