Assertion : $t$ -Butyl methyl ether is not prepared by the reaction of $t$ -butyl bromide with sodium methoxide.Reason : Sodium methoxide is a strong nucleophile.

In Williamson's ether synthesis, if a tertiary alkyl halide (like $t$ -butyl bromide) is used, elimination occurs instead of substitution. This is because alkoxides (like sodium methoxide) act as both strong nucleophiles and strong bases. The reaction yields 2-methylpropene as the major product. Both assertion and reason are true, but the reason for the failure is the basicity of the methoxide leading to elimination, not just its nucleophilicity.