what is 425950 in scientific notation

You put one digit before the decimal point and all the rest after it.  Then multiply the number by 10 to the power of however many places you moved the decimal point to the left. So for this problem, since you moved the decimal point 5 places to the left:

$${\mathtt{425\,950}} = {\mathtt{4.2595\times 10^{5}}}$$