<u>Answer:</u> The element represented by M is Strontium.
<u>Explanation:</u>
Let us consider the molar mass of metal be 'x'.
The molar mass of MO will be = Molar mass of oxygen + Molar mass of metal = (16 + x)g/mol
It is given in the question that 15.44% of oxygen is present in metal oxide. So, the equation becomes:

The metal atom having molar mass as 87.62/mol is Strontium.
Hence, the element represented by M is Strontium.
The correct answer is - C. Hydrosphere; geosphere.
The hydrosphere is the sphere which contains all the waters on the planet Earth. The geosphere is the sphere that contains the solid rocky part of the Earth. When the water goes through the porous sediments and enters deeper into the ground, that means the we have an interaction of water and rocks. In other words, since the water is part of the hydrosphere, and the rocks are part of the geosphere, we have an interaction between the hydrosphere and the geosphere.
What two substances are always produced by a neutralization reaction? water and salt