A quiz question

Using the IXmlSerializable interface, create a class that will serialize XML to be exactly the same as the following:

 <ns1:Root xmlns:ns1="urn:myrootnamespace">
    <ns2:child xmlns:ns2="urn:mychildnamespace">
        <ns2:elementInChildNS />
        <ns1:elementInRootNS />
        <elementInNoNS />
    </ns2:child>
</ns1:Root>

I couldn’t do it