Aclassmate finds that it takes 1.090 seconds for a tossed ball to touch ground. how many significant figures are in this measurement? a) 4 b) 3 c) 2 d) 1

Option A: 4.

In a number, to determine the number of significant figures following 3 rules are used:  

(1) The digits which are non-zero are always significant.

(2) Any zeros between two digits which are non-zero are significant.

(3) In the decimal portion, trailing zeros are significant.  

The number is 1.090, it has two non-zero digits, 1 zero in between two non-zero digit and one trailing zero thus, all of them are significant figures.

Therefore, it has 4 significant figures (underlined): 1.090

i just learnt this recently but i need to look through my notes again