Answer
5
Work Step by Step
$(2.5\times10^{6})(2\times10^{-6})$ $\longrightarrow$ associative property
=$(2.5\times2)(10^{6}\times10^{-6})$ $\longrightarrow$ multiply; add exponents if the base is the same
=$5\times10^{0}$ $\longrightarrow$ if the exponent is 0 the result is 1
=$5\times1$
=$5$