In the matrix \(A=[a_{ij}]_{2\times3}\), what does \(i\) represent?

Correct answer: Row number

In the notation \(a_{ij}\), the first index \(i\) denotes the row number (row index) and the second index \(j\) denotes the column number (column index). For example \(a_{21}\) is the element in row 2, column 1. Thus option B is correct. Option A is wrong because the column index is \(j\), option C is incorrect because the total number of elements is \(2\times3=6\) which is not what \(i\) denotes, and option D is wrong because the matrix name is \(A\). Exam tip: remember the convention a_{ij} → i = row, j = column (first index = row).