Which one of the following elements posed a challenge to Newlands 's law of octaves ?
`Li, Be , B , C , N , O ,F , Ne , Na`

Explanation

Newland's law of octaves states that when elements are arranged order of increasing atomic weights then the every eighth element resembles the first one . But when inner gas (Ne was discovered. Then it was the ninth which resembles the first one . Therefore the element inert gas Ne posed a challange to Newlands's law of octaves.