In an expression \( a \times 10^{b} \).
\( b \) is order of magnitude for \( a \ge 5 \)
\( b \) is order of magnitude for \( 5 < a \le 10 \)
\( b \) is order of magnitude for \( a \le 5 \)
\( a \) is order of magnitude for \( b \le 5 \)