A protein molecule's diameter is measured as 42 Å using X-ray diffraction. If another measurement instrument gives the diameter in picometers (pm), and the ratio of the two measurements is $\frac{x}{10}$, what is the value of $x$?

The speed of light is approximately $3 imes 10^8$ m/s. If a star is 4 light-years away, what is its distance in kilometers? (1 light-year = distance light travels in one year)

The ionization energy of hydrogen is 13.6 eV. Express this energy in joules per mole using the following conversions: 1 eV = $1.602 imes 10^{-19}$ J and Avogadro's number = $6.022 imes 10^{23}$ $mol^{-1}$.

A protein molecule's diameter is measured as 42 Å using X-ray diffraction. If another measurement instrument gives the diameter in picometers (pm), and the ratio of the two measurements is $\frac{x}{10}$, what is the value of $x$?

The density of a substance is given as 0.8 g/$cm^3$. Convert this density to kg/$m^3$.

A chemist measures a reaction rate as $2.5 imes 10^{-3}$ mol L$^{-1}$ $s^{-1}$. Express this rate in molecules $cm^{-3}$ $\mu s^{-1}$ (molecules per cubic centimeter per microsecond). Avogadro's number = $6.022 imes 10^{23}$ molecules/mol.

The Planck constant is $6.626 imes 10^{-34}$ J s. Express this in units of eV s (electron-volt seconds), given 1 eV = $1.602 imes 10^{-19}$ J.

Pressure gradient has the same dimension as that of