Final answer:
The number of significant figures depends on the position of zeros in the number.
Step-by-step explanation:
A. There are 1 significant figure in 400,000. Zeros at the end of a whole number without a decimal point are not considered significant.
B. There are 3 significant figures in 0.000600. Zeros before the first non-zero digit are not significant.
C. There are 4 significant figures in 21,995,000. All non-zero digits and zeros between non-zero digits are significant.
D. There are 4 significant figures in 0.05050. Zeros between non-zero digits are significant.