Determining the number of elements in an array is a common task in programming. In this case, we are given four options: length(), size(), count(), and sizeOf(). Among these options, the correct method to determine the number of elements in an array is the length() method.

The length() method is a built-in function in many programming languages, including Java, C++, Python, and JavaScript. It is used to return the number of elements in an array or the length of a string. The length() method retrieves the size of the array, which represents the number of elements it contains.

Here is a detailed explanation of the given options:

a) length():
The length() method is used to determine the number of elements in an array or the length of a string. It is a standard method in many programming languages and can be applied to arrays, strings, and other data structures. This method returns the count of elements in the array.

b) size():
The size() method is not a standard method for determining the number of elements in an array. It is commonly used with data structures like lists or sets to return the number of elements they contain. However, it is not applicable to arrays in most programming languages.

c) count():
The count() method is not a standard method for determining the number of elements in an array either. It is often used in specific contexts, such as counting occurrences of a particular value in an array. However, it does not provide the total count of elements in the array.

d) sizeOf():
The sizeOf() method is not a valid method for determining the number of elements in an array. It is not a built-in function in most programming languages. The sizeOf() method is sometimes used to calculate the size of a data type or the memory occupied by an object, but it does not provide the count of elements in an array.

In conclusion, the correct method to determine the number of elements in an array is the length() method. It is a standard function in many programming languages and specifically designed to provide the count of elements in an array or the length of a string.