In order to compute mean, you have to add all values of the data set up and divide by the number of data values there are.
In this case, the total sum of all data values is: 81+88+69+65+87=390
The number of data values is 5
To compute mean: 390/5=78
The mean height of the corn stalks is 78cm (C)
Answer:
The correct answer is: X is nitrogen dioxide, and Y is a metal oxide
Explanation:
Combustion of compound of containing nitrogen and metal will give nitrogen dioxide and metal oxide as product. During combustion reaction a compound reacts with oxygen in order to yield oxides of elements present in the compound.
The general equation is given as:

Hence, the correct answer is :X is nitrogen dioxide, and Y is a metal oxide.
Number of valence electrons
Group 2 elements are the alkaline earth metals