LOS ANGELES (Reuters) - Hip hop star Nas scored his sixth No. 1 album on the Billboard 200 album chart on Wednesday with "Life Is Good," knocking off last week's chart topper, Zac Brown Band. "Life Is Good," the 10th studio album from the New York rapper, sold 149,000 copies in its first week according to Nielsen SoundScan. Nas' last solo effort, 2008's "Untitled," also debuted on top of the album chart with 187,000 copies sold. Country music collective Zac Brown Band dropped to No. 2 with "Uncaged" selling 78,000 copies in its second week of release. ...