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

you need to take a look at the periodic system in order to sort these elements into pairs that would most likely exhibit similar chemical properties. first, you need to find elements that are found in the same group (groups are vertical in the periodic system), and then to see whether they have the same valence number. if they meet these criteria, they will have similar properties.

the first pair: ne (neon) and kr (krypton), are noble gases found in group 8

the second pair: li (lithium) and k (potassium), found in group 1

the third pair: s (sulfur) and te (tellurium), found in group 6

answer; the numbers of valence electrons in the acetic acid molecule (ch3co2h) is 24;