Change the following data into scientific notation.  0.000 421 ga.4.21  ´  10–4  gb.4.21  ´  104  gc.42.1  ´  10–4  gd.42.1  ´  104  g

The decimal point is moved 4 places (right) to put the number into scientific notation form. That form is usually written

... a. 4.21 × 10⁻⁴ g

The tick mark is a non-standard notation that would need to be described to anyone you intend to communicate with. Usually, some indicator of exponentiation is used with the exponent, so that 10-4 is not taken to mean 6. More conventional text form for the number would be 4.21*10^-4, where an asterisk (*) is used to indicate multiplication and a caret (^) is used to indicate exponentiation.

You can get a clue from the expanded form of the number:

0.000 421 = 0×10⁰ +0×10⁻¹ +0×10⁻² +0×10⁻³ +4×10⁻⁴ +2×10⁻⁵ +1×10⁻⁶