An electron micrograph of a eukaryotic cell reveals a nuclear envelope with a double-membrane thickness of 4.2×10−2 μm4.2 \times 10^{-2}\ \mu\text{m}4.2×10−2 μm.
Which of the following is this thickness expressed in nanometres (nm\text{nm}nm), written in standard form?
4.2×10−5 nm4.2 \times 10^{-5}\text{ nm}4.2×10−5 nm
4.2×10−1 nm4.2 \times 10^{-1}\text{ nm}4.2×10−1 nm
4.2×101 nm4.2 \times 10^{1}\text{ nm}4.2×101 nm
4.2×102 nm4.2 \times 10^{2}\text{ nm}4.2×102 nm
