Significant Figures In a measurement, significant figures consist of the digits definitely known + one estimated digit.
In the example above, measurement A is definitely beyond the 7cm mark and the 0.8cm mark. By looking
carefully, we can estimate that the measurement is halfway between 7.8cm and 7.9cm, so the final
measurement is 7.85cm. This measurement has three significant digits.
How would you record measurement B with three significant digits?

The answer is d- principle of faunal succession.

27. =3,500,000 x 4,000 = 14,000,000,000

Vander waals forces are inter molecular bonds that exist within molecules of the same substance. a water molecule is made up of oxygen and hydrogen atoms which share electrons between each other. the vander waals forces are forces that exist between multitude of different  molecules of water. dipole dipole forces is the type of vander waals force that exist in water. the oxygen atom which is more electronegative pulls the shared electron closer to itself thus generating a partial negative charge while the hydrogen acquire a partial positive charge. these two different charges causes attraction to occur in water molecules.

Electron equations of the given changes are as follow,a)                              cu      →      cu⁺²  + 2e⁻b)                              mg⁺²  +  2 e⁻      →      mgc)                              cl⁻    →      cl  +  1e⁻d)                              s  +  2 e⁻    →      s²⁻e)                                o²⁻      →      o  +  2 e⁻f)                              p  +  3 e⁻    →      p³⁻g)                              fe²⁺    →      fe³⁺  + 1 e⁻h)                              s²⁻    →      s⁴⁺  +  6 e⁻