Young’s modulus of steel is 1.9 × 10¹¹ N/m². When expressed in CGS units of dynes/cm², it will be equal to (1N = 10⁵ dyne, 1m² = 10⁴ cm²)

The correct option is 1.9 × 10¹².

To convert Young's modulus of steel from SI units (N/m²) to CGS units (dynes/cm²), we can use the given conversion factors:
1 N = 10⁵ dyne
1 m² = 10⁴ cm²

Let the given value in SI units be:
$$Y=1.9\times {10}^{11}{\text{N/m}}^2$$

Substituting the conversion factors into the unit ratio:
$$\frac{\text{1 N}}{{\text{1 m}}^2}=\frac{{10}^5\text{ dyne}}{{10}^4{\text{ cm}}^2}=10{\text{dyne/cm}}^2$$

Therefore, to convert the value, we multiply the SI value by 10:
$$Y=1.9\times {10}^{11}\times 10{\text{dynes/cm}}^2$$

Simplifying the exponents:
$$Y=1.9\times {10}^{12}{\text{dynes/cm}}^2$$

Thus, Young's modulus of steel in CGS units is equal to 1.9 × 10¹² dynes/cm².