Alkali and alkaline earth metals along with hydrogen and helium constitute s-block elements . They have low ionization enthalpies and hence exhibit characteristic flame colouration . They have highly negative electrode potentials and hence are strong reducing agents . Their solutions in liquid ammonia are conducting and also act as strong reducing agents than hydrogen , they are usually prepared by electrolysis of their fused chlorides . Their oxides are basic and the basic strength increases down the group . The solubility of carbonates and sulphates of alkali and alkaline earth metals show opposite trends . The carbonates of alkaline earth metals and lithium carbonate decompose on heating while the carbonates of other alkali metals do not decompose on heating . The bicarbonates of both alkali and alkaline earth metals on heating give carbonates .
The basic character of the oxides , MgO , SrO , `K_(2)O , NiO` and `Cs_(2)O` increases in the order :

Options

A. `MgO gt Sr O gt K_(2)O gt NiO gt Cs_(2)`
B. `Cs_(2) lt K_(2)O lt MgO lt SrO lt NiO`
C. `NiO lt MgO lt SrO lt K_(2)O lt Cs_(2)O`
D. `K_(2)O ltNiO lt MgO lt SrO lt Cs_(2)`

Explanation

To determine the increasing order of basic character of the oxides MgO, SrO, K₂O, NiO, and Cs₂O, we need to analyze the basicity of each oxide based on the following factors:

1. **Nature of the Metal**: Basicity generally increases down the group in the periodic table. Alkali metals and alkaline earth metals are known for their basic oxides.

2. **Position in the Periodic Table**:
- **Alkaline Earth Metals**: As we move down the group from Mg to Sr, the basicity increases due to the larger atomic size and lower electronegativity.
- **Alkali Metals**: The basicity of alkali metal oxides increases as we move down the group from Li to Cs.

3. **Comparing Different Groups**:
- NiO is a transition metal oxide and typically has a lower basic character compared to alkali and alkaline earth metal oxides.

Now, let's analyze each oxide:

- **MgO**: Magnesium oxide is a basic oxide but is less basic compared to the oxides of heavier alkaline earth metals.
- **SrO**: Strontium oxide is more basic than magnesium oxide due to its position in the periodic table.
- **NiO**: Nickel oxide is less basic compared to the alkaline earth and alkali metal oxides because it is a transition metal oxide.
- **K₂O**: Potassium oxide is a strong base, more basic than both MgO and NiO.
- **Cs₂O**: Cesium oxide is the most basic among the listed oxides due to the low electronegativity and high reactivity of cesium.

Based on this analysis, we can arrange the oxides in increasing order of basic character as follows:

**Increasing order of basic character**: NiO < MgO < SrO < K₂O < Cs₂O