Which of the following is not a unit of time?

One $\mathring{A}$ is equal to:

Hertz is the unit for

Which of the following systems of units is not based on units of mass,length,and time alone?

The new $SI$ unit of mass $1 \, kg$ is defined in terms of the difference in the masses of two ${}^{133}Cs_{55}$ atoms. One of these atoms is in its ground state and the other is in an excited state that has a frequency of excitation close to $9.2 \times 10^9 \, Hz$. The number of atoms required to get $1 \, kg$ of mass this way is of the order of (Planck's constant = $6.63 \times 10^{-34} \, J \cdot s$; mass of proton = $1.67 \times 10^{-27} \, kg$; Avogadro number = $6.02 \times 10^{23} \, \text{particles}$; speed of light = $3 \times 10^8 \, m/s$).

If ${u_1}$ and ${u_2}$ are the units selected in two systems of measurement and ${n_1}$ and ${n_2}$ are their respective numerical values,then: