Which is the correct ascending order of wavelengths?

We need to arrange the electromagnetic waves in ascending order of wavelength.

The electromagnetic spectrum in order of increasing wavelength is:

$$\text{Gamma rays} \rightarrow \text{X-rays} \rightarrow \text{UV} \rightarrow \text{Visible} \rightarrow \text{Infrared} \rightarrow \text{Microwaves} \rightarrow \text{Radio waves}$$

• Gamma rays: $$\lambda < 10^{-12}$$ m (shortest wavelength)
• X-rays: $$10^{-12}$$ m to $$10^{-8}$$ m
• Visible light: $$4 \times 10^{-7}$$ m to $$7 \times 10^{-7}$$ m
• Microwaves: $$10^{-3}$$ m to $$0.3$$ m (longest among the given options)

$$\lambda_{\text{gamma-ray}} < \lambda_{\text{X-ray}} < \lambda_{\text{visible}} < \lambda_{\text{microwave}}$$

Hence, the correct answer is Option B.