Some of the answers and comments here seem to say that the /k/ in asked is not elided in standard Englishes. To counter this misconception, as well as to through some light on masked and risked, I thought it might be a good idea to put some information here from vetted published sources, and world-renowned professional phoneticians of English.
The following goes for Standard Southern British English (also called RP). It's taken from Practical Phonetics and Phonology by Beverley Collins and Inger Mees, Routeledge, 2008:
The sequence /skt/ has elision of /k/ instead of, or if preceding consonants, in addition to /t/:
- masked gunmen /mɑ:st gʌnmən/ or /mɑ:s gʌnmən/, they asked us /ðeɪ ɑ:st əs/
[Practical Phonetics and Phonology p. 127]
It would seem then that one should be able to extrapolate from this to words like tasked and possibly risked.
However, the following is from Professor John Wells' blog here. It's the entry for Thur 7 September 2006 (in case you want to check out the rest of the entry):
As an ordinary vocabulary item asked, the past tense of ask, is frequently pronounced without the [k]. In its LPD entry I write it as "ɑːskt", showing by the italicization that the velar plosive can be omitted. If it has no [k], it is homophonous with arsed, which explains our eggcorn.
Although we are very ready to elide the [k] in asked, we are not so ready to do so in other -sk past tenses: masked, basked, tasked, whisked, tusked. Nor can we readily elide the [p] in clasped, rasped, lisped, cusped. (OK, in rapid speech I concede that they all might go.)
I leave it to the gentle readers here to make of that what they will!