Correct answer is (a) The number of matrices having trace 0 is $37\left(7^6\right)$Correct answer is (b) If one matrix out of all the matrices formed is chosen randomly then the probability that it is symmetric is $\frac{1}{343}$Correct answer is (c) The number of skew symmetric matrices is $7^3$Correct answer is (d) The number of symmetric matrices is $7^6$