 The Nasdaq 100 NDX, -2.08 slumped 1.7 in afternoon trading Thursday, with only 17 of its components gaining ground, after the technology-friendly index ran up 3.3 over the past two days. The indexs biggest gainer was Datadog Inc. stock DDOG, 12.28 , which shot up 14.3 over the monitoring and security software platform company reported before the open better-than-expected fourth-quarter results and provided an upbeat first-quarter sales outlook. 