When comparing the basic character of oxides, we must consider several factors, including the position of the metal in the periodic table and the nature of the oxide (whether it is ionic or covalent). Basic character generally increases as you move down a group in the periodic table due to the decrease in electronegativity and the increase in metallic character. Basic character also tends to be higher in oxides of metals as compared to those of nonmetals.

We have the following compounds to consider: MgO, SrO, K₂O, NiO, and Cs₂O. Oxides of alkali metals (K₂O, Cs₂O) and alkaline earth metals (MgO, SrO) tend to be more basic than oxides of transition metals (NiO). Within each group (alkali and alkaline earth metals), the basic character increases as we move down the group. This is due to the larger atomic size and reduced ionic character, making the oxide ion ($$ O^{2-} $$) more able to accept a proton.

Among the given oxides:

• Alkali metal oxides (K₂O and Cs₂O) are generally more basic than alkaline earth metal oxides.
• In the alkaline earth group, beryllium and magnesium oxides behave more amphoteric and less basic compared to oxides of calcium, strontium, and barium. So, SrO is more basic than MgO.
• For alkali metals, cesium oxide (Cs₂O) is more basic than potassium oxide (K₂O) due to being further down the group in the periodic table.
• Nickel oxide (NiO), being a transition metal oxide, is generally less basic compared to oxides from either the alkali or alkaline earth metals.

Therefore, the increasing order of basic strength for these oxides is:

$$ \text{NiO} < \text{MgO} < \text{SrO} < \text{K}_2\text{O} < \text{Cs}_2\text{O} $$

This order reflects moving from transition metal oxides to more typical alkaline earth metal oxides, and then to more basic alkali metal oxides, with the basicity increasing significantly as we move from lighter to heavier elements within each metal group.