Proportions of elements with given 2-part order in finite classical groups of odd characteristic

For an element $g$ in a group $X$, we say that $g$ has 2-part order $2^a$ if $2^a$ is the largest power of 2 dividing the order of $g$. We prove lower bounds on the proportion of elements in finite classical groups in odd characteristic that have certain 2-part orders. In particular, we show that the proportion of odd order elements in the symplectic and orthogonal groups is at least $C\mathrm{/}{\mathrm{\ell }}^{3\mathrm{/}4}$, where $\mathrm{\ell }$ is the Lie rank, and $C$ is an explicit constant. We also prove positive constant lower bounds for the proportion of elements of certain 2-part orders independent of the Lie rank. Furthermore, we describe how these results can be used to analyze part of Yal\c{c}inkaya’s Black Box recognition algorithm for finite classical groups in odd characteristic.