### Brain Teasers

# Three the Hard Way

Using the Periodic Table, and the table alone, without any in-depth knowledge or insight, I challenge you to tell me the missing members of the unique group of elements below.

Group: As, Dy, Ir, Ra, Cs, Ti

Given:

1. The saying about felines would not be false if they had as many lives as this group has members.

2. Cs [Cesium, or Caesium] is in the middle of the group, when placed in order of what gives the members their membership. (Let's call these their "membership cards".)

3. There is ONLY ONE member in this group that is missing which, if their "membership card #" is squared, will give you a year in the 20th century in which the second digit is a perfect square, the third is the square root of that perfect square, and the last is a multiple of the square root of that perfect square.

4. "Those Extremely Smart go to the rear of the group, please".

What's missing from the group?

Group: As, Dy, Ir, Ra, Cs, Ti

Given:

1. The saying about felines would not be false if they had as many lives as this group has members.

2. Cs [Cesium, or Caesium] is in the middle of the group, when placed in order of what gives the members their membership. (Let's call these their "membership cards".)

3. There is ONLY ONE member in this group that is missing which, if their "membership card #" is squared, will give you a year in the 20th century in which the second digit is a perfect square, the third is the square root of that perfect square, and the last is a multiple of the square root of that perfect square.

4. "Those Extremely Smart go to the rear of the group, please".

What's missing from the group?

### Answer

Solution:Na(11) Ru (44) Es(99)

Explained:

There are only NINE elements on the Periodic Table whose ATOMIC NUMBER is composed completely of a DOUBLE:

Na (11) Ti (22) As (33) Ru (44) Cs (55) Dy (66) Ir (77) Ra (88) Es (99)

1. If cats had 9 lives, the saying would be true. The group has 9 members out of 103 elements. (Easy Start)

2. Cs [Caesium, or Cesium] is in the middle of the group, when placed in order of what gives the members their membership: out of 9 members, it would be number 5.

3. No other member in this group has an atomic number that, when squared, gives you a year in the 20th Century. (Try it). 1936 is the year in the 20th Century (based on the "membership card #" being squared) in which the second digit is a perfect square, the third is the square root of that perfect square, and the last is a multiple of the square root of that perfect square. 1936 is equal to 44 squared. (44 would be the "Membership Card #" for Ru (Ruthenium), because its atomic number is 44).

4. Einsteinium, named after Albert Einstein, will be last, with its atomic number being 99. "Extremely smart people to the rear of the group, please".

(No clue provided for Na)

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