I don't really know how to say this, I was in my room when I heard a church singing the national anthem and pledge before the commencement of their normal service. please is it appropriate to do that in church.

If it is America national athem it is not a sin

But if it is Nigeria athem it is an unforgiveable sin

why did Jesus paid his tax. it is a civic duty to honour ur country

That is a disgusting practice. It is one thing for Christians to have secondary loyalties to their nation, and to even be proud of their nation... but for the local church to come together and sing the nation's praises is out of line. And this is coming from a US Army chaplain who leads worship in an Army chapel on an Army installation! I don't even fly an American flag in my chapel during worship, because what unites us and identifies us as Christians is our relationship to Christ, not to a particular nation state.

As I challenged my congregation this morning: we ought not think of ourselves as American Christians, but as Christians who happen to be American. (Or in your case: you are not a Nigerian Christian, but a Christian who happens to be a Nigerian.)