Using the elements -3,-2,-1, 0,1,2,3, and then which are following are false 

1) number of 3x3 matrices  $=7^9$
2) number of 3x3 Skew symmetric matrices  $=7^3$
 3) Trace is zero 
$\Rightarrow$  diatonal elements  $\begin{array}{l}1,2,-3\\ -1,-2,3\\ -1,-1,2\\ 1,1,-2\\ 0,0,0\\ -1,1,0\\ -2,2,0\\ -3,3,0\end{array}\}37$
Remaining elements = 7⁶
4) all diagonal elements are equal and remaining are zero
Then number of scalar matrices=7