<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.
Ca3N2+3MgCl2 (double replacement)
Na = 23 x 2.40 = 55.2
O = 16 x 2.40 = 38.4
H = 1 x 2.40 = 2.40
55.2 + 38.4 + 2.4 = 96
2.40 mol of NaOH = 96 amu
Answer: Neon
Explanation: The second period involves elements with n =2 i.e. the elements have electrons in second shell. The element with filled s and p orbitals will have outer electronic configuration 
Thus the element with filled orbital will be a noble gas. It will have total of 10 electrons and the element will be neon with complete outer electronic configuration will be:
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