quel que

Example

Quelle que soit ta décision, je la respecterai.

Do not write

Quelque soit ta décision, je la respecterai.

Why

Quel que is written in two words and AGREES with the subject that follows: quel que, quelle que, quels que, quelles que. It is always followed by être in the subjunctive. Written as one word, quelque is a determiner, and that is the most frequent mistake with this phrase.